We measured the amount of noise produced at a distance of 10 cm at two different loads, 120W and 350W. 30 dB(A) is the lowest we are able to measure, and values in this vicinity mean that a PSU is inaudibly silent. Everything below 35 dB(A) is extremely silent, and above this level you will start to hear the power supply. At 40 dB(A) and higher the PSU is clearly audible.
In this area the OCZ Fatal1ty 1000W doesn't shine as bright. Its 38.9 dB(A) with a light load and 39.1 dB(A) with a high load is unfortunately not very quiet.