The good thing with pc fans is that they are available in different sizes to a certain degree, and with a multi-volt adaptor running them you can dictate their speed. You are better paying a few $'s more for more silent rated ones. If you check out ebay there's loads and some adverts have their noise in db listed too.
I think this guy got carried away! VVVVVVVVV
http://blog.wired.com/gadgets/fan_pc_3.png