FM575

I have a 97 LS400, recently had all 4 disc brakes done at a dealer ($680). Shortly after there is a rubbing noise coming from the passenger rear only when I brake. The dealer inspected the bakes several times and never found any problems. I had a mechanic friend dissassemble the rear brake and found nothing out of the ordinary, the parking brake drum was slightly worn and within specs. White lube was placed where there looked like some rubbing in the drum area. The problem still exists. Abyone else encounter a problem like this?? or any suggestions???