http://forums.procooling.com/vbb/sho...&threadid=7314
I'm hoping to get an automotive blower (running quietly at 5 volt), but a motorized impeller would be ideal.
You can silence the motor, but the air flow noise, you'd have to fix by adding some kind of turbulators, something to disrupt the airflow. If that doesn't work, you'll have to try another airflow rate: the whistling noise either comes from the air hitting the core, or from within the core.
For some airflow data, check out Bill's radiator roundup on overclockers.