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 - Past: E36 328iC, E46 330ci M-Sport (Imola Red/Alcantara)
Summer: 350Z - Tein MonoFlex coilovers, Impul headers, 06+ front end, 3.90 final drive
Winter: E36 328i - BC coilovers, BBS RA, M3 brakes, M50 manifold, Dinan intake, 3.23 LSD