Rear End Squeak HELP Diagnose Please

[GMKON]

Hello all I have been a lurking around the forums for a while and thank for all the posts a lot have helped me out, however I m in a strange situation I have a 2001 Yukon 5.3 and the past month I had brand new rear brake pads and rotors after a couple of weeks I got new tires and a differential oil and gasket change, the next day I notice a squeak in the rear of the car however it goes away after once I hit the brakes even gently, but when its rolling its always squeaking. We got it on a lift nailed the noise to the passenger rear wheel. Once we spun the wheel the squeaking started, checked the ebrak shoes and all was good replaced the rotor anyways and adjusted dust shield still same issue squeaking its incredibly close to the wheel area but idk mechanic said it needs a whole new rear end diff and all thatt, well car has 220k on it but never towed anything in its life and its pretty well kept I dont see how after I got tires and diff service this happened it was perfectly fine before, also what I noticed on the lift is when it was rolling the other wheel seemed to have more power, wheel bearing seemed good no shaking or nothing like that. It is a consistent squeak and now I cant drive the car because its too embarrassing, driving is good seems to drive fine just the noise ujoints maybe? but its not a clunk it just a squeak 

[tramz]

Take a close look at the abutment shims on the pads.  Its possible they're not centered and making slight contact with the rotor.