I had the sway arm replaced the other day. Same kind of noise (clunk noise). The part was $44 at BMW. Car now rides like new.

The part I am talking about is # 7 in the diagram. Easy to replace (mine was done by the mechanic while I was getting new brake rotors). Just identify if it is the left or rifght side.

Good luck.

http://www.realoem.com/bmw/showparts...23&hg=31&fg=10