Gives the sound a really weird whiny cat cry sound. Sounds nothing like any N54 that I’ve ever heard. Including the one in my driveway. I have relocated inlets ( basically race air filters ) and all the bolt ons you can think of on my 2008 335i ( same engine 'n such ) pushing around 700whp and mine sounds NOTHING like this.
Here’s what a N54 car should sound like >> https://www.youtube.com/watch?v=-AWYDNwI8O4&t=70s and this one has pretty much the loudest exhaust you can get on it
Another good example >> https://www.youtube.com/watch?v=9YIjSiYyfhs&t=73s
This is especially noticeable when decelerating. Really annoying. Sounds like the air filter upgrade effect is just too much. This isn’t the only car that is affected by this either. Pretty much every sport and race air filter upgrade sounds wonky. I can’t make a big bulk ticket for that tho. 
I would also like to point out that this platform does not have a blow off valve in stock form. It has diverter valves. Fine to have this sound when the turbos are upgraded tho.