I would recommend a quieter power supply. I cheaped out and now I am going to get a BeQueit Dark Power.
I agree with this. I bought a Seasonic X Series 750W KM2 80PLUS Gold Fully Modular w/ Hybrid Fan
. The fan only turns on when the PSU gets over a certain load so during most times aside from gaming, the fan is off.
The loudest component in my system is a 20cm Bitfenix case fan (i replaced the horribly loud Corsair case fans). I'm still looking at ways to reduce the noise for it as well (i believe my system sounds slightly louder than my old one solely because of this case fan).
My idea is to move the case fan from the top of the tower to the front intake, then add 'loose' sound dampening material to the top grille area closing in the case a bit more.
If that doesn't work, i might go looking for a different fan controller (possibly even just software). Presently the Corsair Graphite case has a fan controller knob and i've got it turned down to nothing (but it apparently only lowers the fan output to 30% so you cannot go down to 0% power understandably).