Resurrecting this. My '03 E53 with 188k is doing the "clunk" when putting it in drive (sometimes) or reverse (more often). It's more pronounced when on a grade. It's most pronounced when backing up an inclined curve. It also does the "clunk" when going from drive to park facing downhill.

FWIW, rear subframe bushings and most suspension parts are <1 year old.

Did you ever figure out the culprit / solution?