Re: how to make an engine quieter/stealth
It sounds like you've got a few things causing the noise. Something I just heard about today from somebody is lubricant you add to your oil to coat the metal surfaces of your motor. From the reviews I've read online it's a practically a miracle product that reduces noise and improves gas mileage. You should probably make a list of things that could be causing noise and check them individually.
My first thought is your mounting is loose which is causing the high RPM noise. If it's only loud at wide open throttle, it sounds vibrational which more easily fixable. I don't know why the gear housing might whine though.