Including the heatsink fan, I have 5 fans in my computer. Needless to say it stays nice and cool, but it kind of sounds like a nuclear reactor coming online. Overall the fans I added are quite quiet, though they are only a year old.
If I were you, I'd either get new fans, or try what Gnash suggested. That, or you can build an acrylic case, remove all the fans, and submerge your computer (minus power supply and optical drive) in mineral oil, distilled water. Not terribly convenient, but all your geeky friends will find it fascinating