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Why Your Car Is Making a Rattling Noise, and What to Do

By Stephen Fogel, January 9, 2018

It's unnerving. You start your car and hear a rattling noise you’ve never heard before. Your mind starts racing, trying to figure out what the noise is and how bad a problem it will be. 

Is your car going to break down? Does it need a repair — maybe an expensive one? Let’s slow down and take a look at what might be causing the noise. Figuring this out will help your mechanic pin down the repair — assuming it’s not a simple fix you can take care of.

Lots of potential causes

Rattling noises can be caused by a variety of issues. You may hear them when you start your car, when you drive it or when you apply the brakes. They may occur only when the engine is cold, or when it’s fully warmed up. Rattles may happen only upon acceleration, deceleration, going over bumps, rounding a corner, or during some other specific set of circumstances. But whatever the source, it should be tracked down and identified before it gets worse. 

Some rattles are minor and easily fixable. Some are symptoms of future problems that can be headed off with some immediate attention. And some can be the last-minute warning of an imminent mechanical failure. Let’s explore.

Where is the rattling noise coming from?

The first step toward dealing with a rattling noise in your car is to identify where it’s coming from. This will help you or your mechanic find the source of the noise. To simplify this process, we’ve broken down the possible locations to four main areas of your vehicle:

Get it diagnosed by a professional

Rattling noises underneath your vehicle

Rattling noises that come from the bottom of your vehicle may be noticeable upon starting, while driving at certain speeds, when you hit a bump in the road, or even all the time. Here are some possible sources:

Loose exhaust system

Your exhaust system runs from your engine to the rear of your vehicle. It’s made up of several components including the catalytic converter, the muffler and sections of exhaust pipe. Over time, these components can wear and the joints holding them together can loosen. This can cause a rattling noise under the vehicle. The exhaust noise may also be louder than normal, and appear to be coming from under the car instead of the tailpipe at the rear. If the exhaust system is loose, it can also bang against the underside of your vehicle when you hit a bump.

Solution: Have your exhaust system checked by your mechanic or a muffler shop. The fix could be as easy as tightening a loose clamp or replacing a damaged rubber hanger. It’s also possible you might need to replace a section of rusted-out exhaust pipe or even the muffler. Either way, it’s a quick and easy fix. Don’t delay if you suspect the exhaust system is the problem — the consequences could be deadly if exhaust leaks into the interior while you are driving. 

Bad catalytic converter

The catalytic converter is the part of your exhaust system that controls emissions. It converts the toxic gases and pollutants in your exhaust gas into less dangerous substances. The converter can be damaged by thermal shock or an impact, which can cause part of its internal structure to break off and cause a rattle. In extreme cases, this can sound like a box of rocks being shaken. The converter doesn’t fail by itself; something has to cause it to fail, and that should be identified before it is replaced. A bad converter can also trigger your check-engine light to come on and create a trouble code in the engine computer.

Solution: Replacing your catalytic converter is a straightforward procedure. Keep in mind that the converter itself can be expensive, depending on where you live and how stringent the emissions regulations there are (we’re looking at you, California). But, keep in mind that the catalytic converter typically comes with a warranty that’s longer than the basic one for your car. 

Loose or rusted heat shielding

As emissions regulations have gotten tighter, engines and exhaust systems have been operating at higher and higher temperatures. This has led to the need for heat shielding on exhaust components like mufflers, catalytic converters, and exhaust piping. The role of the heat shielding is to reflect the intense heat of the exhaust system away from the bottom of the vehicle. These heat shields are made of thin pieces of metal, and are placed between these components and the underfloor of the vehicle. They have become a common source of rattling noises under the car. Over time, heat shields can rust out or become loose and get detached from their mountings.

Solution: Check the heat shields under the car for looseness and corrosion. Tighten them down if they’re loose, or get them replaced if corrosion has compromised their structural integrity. Driving without them is not an option.

Rattling noises in your wheel wells

Your car’s wheel wells are where your wheels, tires, brakes and most suspension components live. They are located at the four corners of your vehicle. Rattling noises in the wheel wells usually come from a few specific areas. Let’s run down the possibilities.

Suspension parts

Your vehicle has many interconnected components in its suspension system. There are springs, struts or shock absorbers, sway bars and links that are attached to one another. Your steering system is also integrated into the front suspension. When they’re all operating properly, you get a smooth ride and controlled cornering. As your suspension parts wear and age, you may hear rattling noises from the wheel wells. Some causes for these noises can be:

  • Worn-out suspension struts or shock absorbers
  • Loose or worn bushings — these are a kind of cushion in your suspension system
  • Damaged or bent suspension components
  • Loose sway bar link

Solution: A mechanic should thoroughly inspect your suspension system. Unless your struts are leaking oil, or something has become detached and is obviously hanging loose, you probably won’t be able to diagnose the problem. The remedy can be something as easy as tightening up a loose connection or replacing a bushing. You may also need to replace your worn-out struts or other damaged parts as necessary. Don’t put these repairs off — a reliable suspension and steering system is important to your safety.

Brakes

Your brakes are complex mechanisms that attach to the suspension where the wheels and tires are attached. The brakes supply the stopping power that slows down the wheels when you apply them. Most brakes today are disc brakes, which use friction pads to press against a flat disc (or brake rotor) that rotates along with each wheel. As the pads press on the brake rotors , they slow down and stop the vehicle. 

Over time, the pads wear down and need replacement. If you do not change your brake pads you’ll end up with metal-to-metal contact, which gives you very poor braking, plus some scraping and grinding noises as you destroy your brake rotors, other brake system components, and risk not being able to stop.

Other possibilities could be missing or broken brake pad anti-rattle clips, or using inexpensive brake pads. The anti-rattle clips keep the pad from rattling when not braking. Inexpensive brake pads may not fit and could be loose, also causing them to rattle. 

Solution: Take the car to your mechanic immediately — you should avoid driving a vehicle with noisy brakes. The mechanic will diagnose the problem and repair your braking system. You may need new brake rotors, new pads and perhaps some other components, depending how much damage has been done. 

Wheels and tires

Occasionally, the lug nuts or bolts that secure your wheels onto the car can come loose. If a few of these nuts or bolts get very loose, you may hear a rattling noise caused by the wheel moving around on the hub. If you have wheels that are covered by hubcaps, a loose lug nut can make a rattling noise as it bounces around inside the hubcap.

Other causes could be a loose hubcap or a loose brake backing plate — the shield behind the rotor.

Solution: Stop your car immediately, set the parking brake and check that the wheels are securely attached. Grab each tire with your hands at the 10 o’clock and 2 o’clock positions and rock the tire in and out to check if it is loose on the hub. If you detect any movement, get out your lug wrench and tighten up all the nuts on that wheel. If this situation has been going on for long enough, the threads on the lugs may be damaged and can no longer be tightened. In this case, you should have your vehicle towed to your mechanic to have the lugs, and any other damaged items, replaced.

Rattling noises under the hood

Your engine, transmission and several ancillary systems all reside under the hood. There are many different mechanisms, operating together and individually, to keep you moving down the road. As a result, there’s a wide variety of sources that can cause rattles.

Oil and fuel-related noises

Let’s start with rattling noises under the hood that are caused by oil or fuel-related problems:

Low Engine Oil Level

Your engine oil pump circulates motor oil through the engine, lubricating the internal moving parts. Over time, the engine can consume, burn or leak oil. If the oil level gets too low, you can have a situation where the oil pump sucks air into it and the air gets pumped through the engine along with whatever oil is remaining. This can cause a rattling or ticking noise from within the engine.

Solution: Shut off the engine immediately. Use the oil dipstick to check the engine oil level. Pull out the dipstick, wipe it off with a paper towel, then reinsert and check the level. It should be between the two marks on the dipstick. If the level on the dipstick is low or nonexistent, add the specified oil for your vehicle until it is up to the full or maximum level. If you have a major oil leak or are burning a lot of oil, the cause should be found and corrected. Otherwise, you’re likely headed for an engine failure

Pinging From Low-Octane Fuel

Your engine needs gasoline with the correct octane rating to operate properly. If you hear a pinging or rattling sound when accelerating, low-octane fuel could be the cause. Pinging (also called pre-ignition or detonation) can also be the result of carbon deposits, a bad knock sensor, overheating or incorrect ignition timing.

Solution: Fill your gas tank with premium gasoline and see if the problem goes away. If not, your mechanic will have to track down the exact cause. Get this fixed immediately, because it can damage or destroy your engine.

Noises from internal engine parts

There are many moving parts within your vehicle’s engine that can cause rattling noises. Let’s run down the list:

Timing chain or belt noise

Your engine’s timing chain or belt connects the crankshaft to the camshaft, for proper operation of the valve train as described above. Modern overhead cam engines have very long chains and belts, which use hydraulic tensioners to keep the chain taut. Over time, the nylon chain guides wear and the tensioners can’t manage the slack in the chain or belt. You hear a rattling noise made by the chain or belt whipping around, untensioned, inside the timing chain cover. This noise rises and falls with the engine RPMs.

Solution: Replacement of the hydraulic tensioners and the chain guides is necessary. If you have a timing belt, check it for wear and replace it if you are near the prescribed replacement interval.

Noise from the valve train

The valve train is the system in your engine that’s driven by the camshaft and opens and closes your engine’s valves. The valve train allows fuel into the cylinders and lets the exhaust gases out. The valve lifters are the components that do the actual opening and closing of the valves. They can be either mechanical or hydraulic. If they get worn, stuck or out of alignment, a rattling noise may be heard, especially at low RPMs.

Solution: Depending on the type of lifter and the exact cause, the fix may involve adjusting the valves, using a detergent additive if the lifters are coated with varnish and sticking, or replacing the lifter if it is defective.

Piston slap

If you have a high-mileage vehicle with a worn engine, the pistons may fit in the cylinders very loosely. During a cold start, this may show up as a rattling noise. It typically goes away once the pistons expand from the heat of the engine. 

Solution: Fitting oversize pistons will solve the problem, but this is a very expensive fix. It may not be worth doing on a high-mileage vehicle that has lost most of its value. If you can live with the noise, it is unlikely to cause any further issues.

Rod knock

Your connecting rods are the parts that transmit the rotary motion of the crankshaft to the up-and-down motion of the pistons. Rod knock noises are the result of wear from insufficient or dirty oil, and can wear down the surfaces of the bearings. This causes excessive clearances between the rods and the crankshaft. 

Solution: Once you hear the noise, you will need major engine work, which will be very expensive. If not fixed, some of all of these rotating parts can fail and destroy the engine.

Rattling noises from items attached to the engine

There are many devices that are attached to and driven by the engine. Rattling noises can come from these mechanisms.

Drive belt issues

Rubber drive belts connect many of the systems driven by the engine. Over time, these belts can deteriorate from wear and the high temperatures in the underhood environment. A frayed or cracked belt may create a rattling-like sound as it flaps around in the engine bay. Or the noise could be caused by oil leaking onto the belt, or misaligned belt pulleys.

Solution: You or your mechanic can replace a worn belt pretty easily. But you’ll want to have a professional look into an oil leak or misaligned pulleys. 

Bad water pump

Your water pump is an engine-driven mechanism that circulates coolant through your vehicle’s engine and heating system. The bearings on the drive pulley can fail and cause a rattling sound. This may be combined with a coolant leak.

Solution: Check the water pump pulley for excessive slack or leaks. If you find either, the pump needs replacement.

Broken harmonic balancer

A harmonic balancer is a counterweight that is used to reduce engine vibrations. It uses a rubber ring for support. This rubber part can separate from the balancer, causing the other parts to make a rattling noise.

Solution: Replace the harmonic balancer.

Defective starter

Your starter motor cranks your engine and gets it started. It has a component called a bendix that connects it to the engine when starting it, and disconnects it when it is done. The bendix can become defective and not allow the starter to disengage from the engine. This creates a rattling noise.

Solution: Replace the starter motor.

Bad fan clutch

If your vehicle has rear-wheel drive, with its engine mounted lengthwise, your engine may have a fan clutch to regulate the operation of its engine-mounted cooling fan. The fan clutch can fail and produce a rattling noise. You may also observe higher coolant temperatures or possibly overheating.

Solution: With the engine off — repeat, with the engine off — check for excessive play by holding the fan and moving it in and out. The fan may also turn in both directions. If it is defective, the fan clutch needs to be replaced.

Other sources of rattling noises under the hood

Because there are so many moving parts under your hood, there are many other sources of potential rattles. These include:

  • A cracked or loose accessory bracket
  • A cracked flex plate between the engine and transmission
  • Worn crankshaft bearings
  • Worn and loose piston pins
  • Loose heat shielding on the exhaust manifold, underhood catalyst or turbocharger
  • Failing idler pulley

Rattling noises inside your car

You may hear rattling noises that come from inside your car. Today’s vehicles have storage spaces throughout the vehicle. These noises are usually due to loose or unsecured items moving around as you drive. Here’s how to track them down:

Glove compartment, door pocket and console noises

Rattling noises coming from your interior storage spaces will usually be noticeable when you hit a bump or go around a tight corner.

Solution: First check the contents of each of these storage spaces. Are there any small but heavy items, such as lug nuts, bolts or tools, that can roll around and make rattling noises? If so, remove them and continue driving. If the noise goes away, problem solved. If not, check the glove box door, the console cover and any moving parts on the door pockets. You may find loose mounting hardware, or something that is out of alignment, causing it to rattle. If you can see an obvious way to fix it, go ahead. Otherwise, have your mechanic take care of it at your next visit.

Trunk and luggage compartment noises

Interior rattling noises that come from the rear of the car can be caused by a variety of different items, and will be noticeable on sharp turns or when you hit a pothole. 

Solution: Open your trunk or luggage compartment and take a close look at everything inside. If the trunk is pretty full, try taking loose items out and see if that helps. In additions to potentially causing rattles, a lot of items in the trunk adds unnecessary weight, and is bad for your fuel economy.

Next, check the spare tire and the jack. Be sure that they are tightly secured and unable to move around. Check around the tire for loose items that can roll and make noise — remove any you find. Now go for a drive and check whether the noise is gone. If you still hear rattling, there is the possibility that the noise could be coming from something loose in your rear suspension. Have your mechanic take a look.

Other interior noises

Nearly anything in your interior with moving parts can get loose and make a rattling noise. Here are a few other sources to check:

  • Cup holders
  • Folding seats
  • Open windows
  • Luggage compartment covers on SUVs and hatchbacks

Solution: Inspect these items for loose or missing hardware. Be sure all folding seats are properly latched. Repair as necessary, or tell your mechanic about it.

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