I have a 2002 Chevy Cavalier and am having rear braking issues. A while back, I noticed a grinding/squealing sound from the rear when I applied the brakes. Occasionally, after I braked and when I would release the pedal, there'd be a thud sound. The thud only happened occasionally and not every time. I had had the front brakes replaced 1 1/2 years prior, but not the back ones, so I assumed my rear pads were shot. Took it into a brake shop here in LA and had an inspection. I was told (and shown) that my rear brake pads still had sufficient material, but that my front pads and rotors were shot. "What about the rear brakes?" I asked. They said the rear was fine and just needed cleaning and adjustment.

I walked out of there $400 poorer, but glad I didn't have to worry about brakes anymore. For a few weeks, it seemed okay, still a little squeaky in the rear brakes, but I was told that was normal. However, last week, while in LA traffic, I noticed that the rear brakes were as problematic as ever, and I also noticed that when I braked, there was a periodic, somewhat quiet knocking sound. I started paying more attention to the brakes (turned off CD player and A/C) and noticed I still had the same issues as before. Squeaking, occasional thud when I released the brakes, and now I noticed that braking causes the car to shake a little. It kind of feels like the front brakes take all the load, because I can stop fine, but it isn't graceful.

I know little to nothing about cars, and other than changing tires, I have no auto expertise. So, the questions are: what are the possible things this could be? Within those, are these things that wouldn't have been apparent by a brake inspection that was performed by the shop I took it to? What I mean is, could the folks at the shop be incompetent and missed it, or could this be a problem that wouldn't have shown up in a visual inspection?