I have an 03 525. A few months ago it developed a noise in the back end when going over bumps (eg road dots or washboard roads). It sounds like someone is shaking a coffee can with a handful of bolts in it. I had the rear shock tower mounts replaced but the noise persists. Anybody got a clue?
on mine it was the calipers. They have rubber pieces they ride in (as breaks wear) and they seemed to wear and get loose. bavauto has these metal inserts and the problem is gone! Hope that is the same issue on yours it is really annoying.