So I found the culprit of this noise. Just for the record if anybody experiences this noise also, it was the exhaust flap opening and closing. I did the golf tee mod and the noise was gone. Although I still doubt that this noise is normal as I haven't heard it in other 335i's that I've driven. Weird thing is though, my dealer swapped out the muffler and the noise did not go away. Anyhow, I love how my exhaust sounds with the golf tee mod now, especially those farts and burbles
. Just a little bit of drone at low RPMs that I can live with.