On my new PC, the component making the most noise is the rear exhaust fan on my case (it is the only exhaust fan in my PC). I tried to disconnect it and watched temperatures in SpeedFan and CPU was usually at about 35C, peaking to about 50C when the system was under load - this doesn't look too bad.
So I'm considering that I'll leave the exhaust fan disconnected permanently after which the computer is very quiet - the only noise-making components are Arctic Cooling Freezer 7 Pro Rev.2 (CPU fan) and PSU fan (Enermax Pro 82+), both being quiet enough as far as I can tell. (My GPU has a passive cooler.) Also, those 2 components are moving parts so will provide some air flow in the case and, even better, PSU fan sucks the air out of the case so it kind of is an exhaust fan in itself.
Does anyone run with the exhaust fan disconnected? You don't have to tell me that it's always better to have more air flow than less, I know that, but the noise is also a consideration for me and temperatures around 40C should be fine shouldn't they?
(I might also consider getting a quieter case fan but I'm specifically interested in your opinion on the no exhaust fan scenario.)