If it bothers you that much, replace it, the PSU needs a fan.
Try adding an exhaust fan to it, a quiet one, like I have.

If that doesn't quiet down the normal fan, and you don't want to replace the normal fan, and it bothers you that much, sell it off and buy an Antec.. my truepower is the quietest part of my system even with the other fans at 5-6v with damping, under full load, and that was before I put the exhaust fan in. They're stable and the EPS one is less than $100.