Hello,
Have you had the rear end inspected for worn suspension?
Have you had a full 4 wheel alignment done at a reputable shop (one that will actually adjust the alignment and not just do a "toe and go"?
(this is when the tech is too lazy to do a full 4 wheel alignment and just adjusts the front toe to put the steering wheel straight)
Well if it was done at a good shop then they should have lifted the vehicle up and inspected the suspension before doing the alignment.
If you have worn suspension, then what ever adjustments were made would go right out of spec as soon as they had taken the car off the alignment machine.
It sounds to me like you have excessive negative camber in the rear.
It is very common for the rear balljoints and trailing arms to get loose on your vehicle. This can be checked by lifting the vehicle up and moving the tire back and forth at certain areas. While moving the tire, you should feel no looseness. If looseness is felt then it has to isolated to the worn componant. (A good mechanic should know how to check for loose suspension. )
I would recommend getting your rear suspension checked for worn / loose trailing arms and balljoints.
When you get your next alignment done, ask for a printout of your vehicle adjustments made. The sheet will show adjustments out of spec in red and adjustments in spec in green. This is just insurance that a proper alignment was done.
BMW Technician
BMW STEP Custom Training, Certified Diagnostic Tech, ASE Certified, State Master Mechanic License