My 2004 4.4 makes the same noise and it drives me nuts. Its been to the dealer twice. The first time they didn't hear it, the second time I drove with the tech and showed him. He seems to think its normal however my folks 2004 3.0 doesn't make the sound and the new X5 I had as a loaner didn't make it either. Pisses me off. I am going to have my local independant BMW guy look at it and then bring it to another dealer. I'd just have the independant guy take care of it but that damn thing is still under warranty.