I think so... Others have commented and I agree, they seem loudest around idle speed. Probably due to the fact that you are sitting still at that point and there is no wind noise to drown them it.
Every once in a while I'd like to push a button and go into "stealth mode" like they did with the helicopter in the show Airwolf. My dad flew helicopters for a living and couldn't bear to watch that show...It was too unrealistic (especially the stealth mode). I guess neither helicopters not motorcycles can defy physics and mute themselves at a touch of a button...Well except other than the kill switch!
