The rear brakes can squeak because the rear brake pad may be contacting the brake rotor. A burr on the backing plate of the brake pad can prevent the pad from seating in the bracket properly causing the contact with the rotor. The backing plate and the pad support hardware can be deburred in the contact areas. Mazda has also released revised brake pads.Google+
Car Problem Reports
Mazda Mazda3 Rear Brakes Squeaking
Mazda Mazda3 Problem
Average Mileage: 43,000 mi (23,000 mi - 62,000 mi)
Took our Mazda 3 in for scheduled maintenance. The service centre said that the break pads, (although only 30% worn, we mainly engine-brake in our manual transmission vehicle), were cracked due to overheating. This seems HIGHLY suspicious to me, to have this problem in a vehicle with only 40,000mi on it that doesn't get driven hard. That is, it's a very rare occasion that we ever hammer on the brakes seeing as we let the engine do most of the braking for us.
I truly believe this some kind of manufacturers default -- which of course, the service centre won't take responsibility for and want us to spend hundreds of dollars to replace them.
Visitor, 2008 Mazda Mazda3, 23,000 mi
The Honolulu Cutter Mazda dealership was unable to hear the squeaking during their test drive. I find this unbelievalbe and asked them if they took it for a test drive. They said the breaks look fine. If I want them to look further, it will cost over $100 to open it up and look. I have an extended warranty on my car, but the warranty company said that they can't tell me whether a repair will be covered until it is opened up and properly diagnosed. My question is, why would I pay the dealer >$100 to open it up for diagnostics if they couldn't even find the squeal upon normal driving (that I hear every day every time I brake).
When braking, the back passengar side makes a low sort of dragging sound