I wonder if it is the same noise discussed here:
To some degree my understanding is that some clunk is normal. I had a first generation CTS V and it suffered from this but it was considered normal and never had any negative effect on performance. BMW had used a different lube in the diffs of cars experiencing this if I am speaking of the same noise; please correct me if I am mistaken.
2009 M3, Silverstone/Black Leather, DCT, Ipod, Sat, 19"'s, Cold Weather, Premium, Tech, carbon roof.