My wife's 2008 X3 3.0si also encounters the same lifter noise. It only occurs occasionally.
I found something similiar over on the e90post forum. It seems like the non-turbo e90 3 series cars experience a similiar lifter noise.
Check the thread at the below link. Apparently there is a process to bleed air pockets out of the lifters.
http://www.e90post.com/forums/showth...t=lifter+noise