With my chiller on full (temp), and the fan throttled back to silent, all I hear, aside from PSU and HD, is the compressor hum (no louder than a fridge) at 1900+ MHz. Need to do some ducting when I set it up again, the 40C exhaust in front of the chiller sucks ass in August. It's welcome in January though.
Almost a 500 Mhz OC last time, and the HP Celeron 900 upstairs made more noise.
...I'll be back.