The thing is that it's a diffuser and not a deflector. I had a deflector in my last 7, and it was much quieter. Not sure about the back passengers, because they're not allowed to complain, but the front compartment doesn't experience any less turbulence in my F01 than it did from the sunroof in my E65. Sometimes I just keep the sunroof open around 70% so that the diffuser doesn't engage. That damn thing is loud enough to drive a sane man over the edge. Maybe those Germans added it in to cover the noise of that garbage stereo they sold us for an extra $1800.
2014 M6 Convertible Individual Citrin Black/Champagne Full Merino - 6MT, Carbon Ceramic Brakes, Exec, B&O, Night Vision, Driver Assist, 15% Tint, Coded
2013 750i Mineral White
2011 750i Jet Black
2007 750i Monaco Blue