check flapper valave in header
my 2010 was making a tremendous racket. i, and the dealer thought it was the cam chain tensioner. when i picked it up, it turned out to be the header, which they replaces, of course under warranty. i asked about the cam chain tensioner failure, to which they replied they have never had one come in. this is a big high volume bmw (only) dealership. nice and quiet now.