second case fan in, the noise is a little bit more and there is a noticeable hum, but i'm sure i'll get used to it. it lowered my idle temp pretty drastically, about 7 degrees. i'd say that's worth it.

my best guess is that the hum comes from all the shit in the way of the fan. the air filter and everything in the hard drive bay. no real way around that until i get a new case, which might just be my next upgrade.