Mine sounds exactly like that, but I am N54 and already had my wastegates replaced. Sound came back about 4K miles later and stayed that way. I gave up and now just pretend its not there for my sanity.
This has to be the most ridiculous thing about these cars. My co-worker bought one recently and a few days after delivery he came in all worried that his car was "knocking" like crazy. After hearing what he was talking about, I was just dumb founded. I thought BMW fixed this crap and only us poor early adopter souls had this? Guess not!
