Our new-to-us '99 328i auto, 100k, has a clunk in the rear-end/diff area. Typically at low speed, typically with load reversal or at least load variance, and no issues at speed. I looked underneath while the wife switched from reverse to drive but saw no relative motion between diff and subframe, nor between subframe and body. Also thankfully no sign of floor failure. From underneath it also sounded a bit metallic, whereas it sounds more rubber-thunky from inside the car. Me thinks that the list of possible causes, in order of declining probablity, is ... diff to subframe bushings, subframe to body bushings, rear U joint, internal diff problem. So my questions is ... what is the most likely culprit and do I have to drop the whole rear package to swap the diff-to-subframe bushings or can they somehow be done in place?