Odd rattling

[nofishfisherman]

Vehicle - 2006 Mazda 3, 104,000 miles.

I recently had brake pads and rotors replaced on all 4 wheels.  Also had 2 new tires put on.

After I got the car back I started to notice an intermittent rattle coming from the back end. Seems to be coming from middle of the back end but perhaps a little toward the passenger side.  It doesn't do it all the time.  Most often it happens in the morning when I first go to drive the car and only happens at low speeds although not all the time.  When I apply the brakes the sound stops and it doesn't happen if I'm in reverse, only when driving forward.  The rattle is pretty loud and when it first starts but does lessen after driving for a little and goes away entirely at higher speeds (above 30 mph).

I've gone under the car and did a quick look but didn't see anything obvious although I have no idea what to look for so thats not surprising.  

So any thoughts on what it could be?  It started right after I got it back from the shop when the brakes and rotors were done.  I plan on bringing it back in but just thought I'd pick your brains for a minute first.  

Edited August 19, 2016 by nofishfisherman

[Jeremy airjer W]

The new pads are rattling in the brackets would be my guess. Either a sub par set of pads was installed that did not come with new shims or the brackets that hold the pads are worn out. It is pretty easy to figure out if this is the problem. Jack up a wheel and whack the tread with a good sized hammer. If you hear the rattle than apply pressure the in inbord pad with your finger and repeat. if you still hear it do the same with the out board pad. If either make the noise go away you found the problem.

[nofishfisherman]

I'll see if I can check that out. Thanks

[nofishfisherman]

Well you were right.  I took the car into the shop over the weekend and had them take a look at things.  The shims that were there were being allowed to rattle and move around due to a part malfunction.  Not exactly sure what failed but the shop repaired/replaced everything under warranty.  

[Jeremy airjer W]

Really common on Mazdas. The first one you run into will drive you nuts, the second one goes a lot smoother.....