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 - Past: Fern Green E36 328iC, Dunkelgruen E36 328i Sedan, Imola E46 330ci M-Sport
Current: 03 350Z - Tein MonoFlex coilovers, Impul titanium headers, 06-08 front end conversion,
3.9 final drive, Tomei test pipes, ChargeSpeed CF trunk lip, SPC camber arms, 5/8" plenum spacer, etc.