Loud Rattle when idle on 1999 Ford Expedition

My car has recently started having a very loud and extremely embarrasing rattling noise when in idle or when I'm going real slow, like through drive through. If I place the car in neutral or park the noise will go away or reduce drastically. There is no rattle when driving at regular speeds. Sometimes when I'm driving slow to turn a corner it will also rattle. The rattling sound is a mettal to mettal type noise ... very loud. Any ideas?

Asked by for the 1999 Ford Expedition
You local Repair shop should perform an inspection of your Exhaust system. Your Catalytic Converter may the cause for such noise. Internal components inside your Catalytic Converter may have separated creating noise. Exhaust shields should be inspected also for broken welds or loose shields.
2 more answers
Take a look At The Muffler Under The Truck Right Past The Crossover Connection Should Be A Clamp There Holding It Correctly Mine Was Loose Because The Shop Did Not Get It Tight... Hope This Helps!!!
I have the same noise, not sure buy my uncle told me its just the heat shield vibrating