How's the tire wear on the rears? If the insides are more worn, you should look into replacing some of the wear parts in the rear suspension; lots of threads around on what to replace if you do some searching.

__________________
2001 X5 Sport 3.0/5-speed
1998 318ti/5-speed
1988 735i/5-speed
1984 528e/5-speed (soon to be M20B25-powered 525i!)