looking at the rearend of a vehicle, viewing the rear tires. you see 3 tread groves on 1 side and 2 on the other. so it looks like the bumber is offset to one side alittle. whats this a sign of? could it be supension related from a car setting for along time on a slight slope? or unibody dmg?

 

is the car Lowered/Raised from the factory height? If so the panhard bar is at a different angle from stock and hence the rerend will get pulled or pushed a bit either way. Lowered/sagging it will go to the Drivers side and raised it will go to the pass side.

Its also possible that if you have not replaced the PHB bushings that they are worn and not holding the rear in place as well as they should.