My first suspicion was motor mounts - see my previous thread: http://www.xoutpost.com/bmw-sav-foru...ml#post1057441

But BMW tested the vac system and that was working within spec, and every mechanic who has physically inspected the mounts has said they look and feel fine. When punching the gas with foot on brake, there is no visible engine movement other than perhaps a cm or so. So I have almost ruled out engine mounts.

Also, the buzz sound (which started after I suspected engine mounts) seems to be related - and I don't think engine mounts could cause that noise without there being alot of engine movement.