[pokernaut]

yes, restriction makes wind turbulence noise. the same effect applies to heater grilles. i had one in right next to my couch in a livingroom that howled like a banshee when i tried to close the vent which didn't seal all the way. to stop it, i taped a piece of cardboard over the vent and it totally stopped it from making any noise and the wide open unit in the corner stayed fairly quiet as it was wide open.

the whole "dimmer" concept doesn't sound bad either. fans DO have a sort of dimmer too at that. most fans have high, medium & low settings on them which basically regulate the power to the motor. i don't know how light dimmers differ. i would think it's just a difference between potentiometers vs. resistors. pots are continuously variable & resistors have set values.

just lower your airflow. if it's that loud, you must be moving alot of air.

another thing you could do is add more ducting like another line or use larger diameter tubing. then, the air would meet less resistance and flow more easily. it's the same idea behind a whistle, the harder you blow, the louder it gets. the less resistance air gets, the quieter it gets like a gentle breeze.

sounds like you're overtaxing the system trying to force too much air through it.