Rear brake problems

["Craig D. Niederst" <niederst@telerama.com>]

I finally get my car back from a 2+ week AC repair, and on the way home I
notice a thudding/rubbing sound from the rear of the car. Upon closer
inspection, the pads look OK, but the rotors look rusty in streaks, even
after some hard braking. Also, the parking brake appears to be working fine.
The thudding/rubbing is there whether I use the brakes or not, but gets
louder when I use them. There was also a rubbing sound from the front left
wheel, and it turned out to be the plate behind the rotor was pushed right
up against the rotor. I was able to correct that, but cannot even find out
what the thudding/rubbing in the rear is. The odd thing is, none of these
problems were present when I took the car in to have the AC fixed. I use
this shop exclusively, so I doubt sabotage comes into play here (but you
never know, I did get the AC part on my own at a $60 savings from Langan).
Any ideas what is causing this thudding/rubbing? TIA.

Craig
'92 100S (71k)