| posts: 9,735 | Location: England
Sounds to me like the bearings on the fan are wearing out. That happens to me with my last Cooler Master V8 CPU cooler fan. Eventually the fan died completely and I had to replace the cooler (since it wasn't easy to replace the fan on the V8).
My last PSUs fan became a bit noisy so I oiled it.
It worked ok for a while bit ultimately it was too worn.
Replaced the fan and all was ok.
Its not hard to do, the fan wire should be socketed.
You can cut the wires off the old fan and solder them to the new one if its a non-standard socket or if its hard wired into the PSU.
Make sure the polarity is correct.