When I installed the Carbonio intake from Randy in my '99 E36 328iC (M52) it was a LOT louder than the stock airbox.
When I installed another Carbonio intake from him in my '04 E46 330ci (M54) it was only a bit louder than the stock airbox, with the biggest difference and really only very noticable being above 5,800rpm.
I guess it depends on the engine, really. That and I could hear a lot more noise with a convertible with the top down than the much more refined E46 with an actual roof, haha.
Damon Choy - 17 years of age - First: E36 328iC Second: E46 330ci M-Sport (Imola/Alcantara)
2003 Nissan 350Z Touring Pkg. - Le Mans Sunset - Black leather - ARC Titanium shift knob
Chargespeed carbon fiber trunk lip - 19" VarrsToen ES 3.2.2 - Impul headers - Muffler delete
Tein MonoFlex coilovers - Tomei test pipe - Toyo R888/Michelin Pilot Sport - Central20 3.9 FD