I honestly cannot hear the fan on my Antec PP303X, but I do have 3 other 80MM fans and a FOP38 (7500RPM 60?mm fan)... I've never actually noticed the sound from the power supply that I can remember, even when first setting up this system (no case fans and a CoolerMaster heatsink and lower output fan). If you have access to a normal 80MM Antec case fan, listen to it. That's about what the power supply sounds like.