Did you or someone else jack up the bac kof the car by lifting it by the rear trailing arms and bent them? If that are dead straight, that will cause all sorts of weird behaviour form the back end.
Lots of people stupidly jack up their car from those trailing arms thinking that they can support the weight of the car - which they can't, obviously.
Just look through your wheel and line up your lsight with the rear most trailing arm (it goes up and intto the middle of the car. if it is curved, then it's bent. But don't mistake itt's dog-bone shape for a defect.
