damric :
Is it running hot? Maybe it's clogged with dust, forcing the fan to spin fast. If dust is caked on the fan blades unevenly it could cause serious vibrations.
IT could be just that the fan is dying. Can you oil the bearing?
It could be dust because my room is very dusty, but I cleaned it out before and no dust usually gets in the PSU for some odd reason. Myy 750D has the worst dust filters in the world (thankfully I am getting rid of it tomorrow, I hate this case). I don't think that it is getting hot, I don't see why it would.
I am not sure how to oil the bearing. I have never really done much with PSU's. It is only a few months old. I have had times where in one game, my PSU makes sounds like it is a musical instrument. But that is in one game only and not common. I can't afford a new PSU (just to let you or anybody else know), since I bought a new motherboard, purchasing custom liquid cooling parts soon, and getting a new case tomorrow.