6th gen clunking noise??

[J05hman]

So i bought a 1996 celica st and after only a couple weeks a clunking sound appeared from the rear. Sounds like its coming from the driver side. The only thing i found was that the calipers seemed pretty loose on the rotor and I could easily rock them from side to side making the caliper pins hit the end and make a noise. The noise is heard when driving slow but cuts out when the break pedal is pressed even slightly (which would confirm the loose calipers). The clunking also speeds up and slows down together with the cars speed. My mechanic said the rear calipers are supposed to be a little loose as they are "floating calipers", which checks out i guess.....

My best guess is the bushings on the caliper pins aren't good enough anymore, or the calipers are just due for a change. Any suggestions for what to investigate before i buy a new set of calipers??