The only time I have heard any noise is when the source is off. I think you guys are making more out of this than is really there. I have four fans cooling my equipment enclosure that make a little noise too. I much prefer a little bit noise than overheated expensive electronics.
Slowing down these fans could work though because they are of excessive CFM for the conditions so a lower RPM could go a long way to quite these things down. A resister in the positive lead could do the trick.
A couple resistors would be needed to create a voltage divider. Choose the correct resistors to create the correct voltage divider ratio (90/10 or 80/20 would work fine). Then move and attach the positive lead of the fan between the resistors and the other lead to ground.
I wouldn't cover the vent holes. They are there for a reason.
Edited by roncruiser - 10/28/13 at 12:51pm