I installed the VRSF downpipe a few weeks ago and have heard this high pitch air rushing sound since I have installed it. I've listened to videos of other N55s with the same set up (Catless DP & stock cat back) and they do not make the same noise at all. I have replaced the turbo gasket and the Vband clamps are next. What baffles me is that this sound only persists for about 10-20 seconds until the engine revs down from the cold start. It also makes a pretty horrible 'turbo spool' noise while driving under light to medium throttle only in Comfort Mode (may be tune related) then again, I have heard no other N55s make.
Looking for any suggestions/Advice
Video link:
My apologies, I am not sure why the video looks like I recorded it on an Ipod Shuffle