Sure it's the PSU fan? usually a system like that has a CPU-fan and a case-fan as well, so those could be the culprits too. You'll have to investigate by turning on the power while the case is open and you're watching/listening closely what's happening where.
You did say you opened the case and the noise was coming from the PSU. But Ath makes an excellent point. There are other fans in a computer case, and many times the case fans, or those smaller high-speed units on drive trays, CPU coolers, and graphics cards can also go bad. So as long as you're in there, it's not a bad idea to check them all.
be really careful blowing compressed air in a psu fan -- do NOT do it while the computer is running.
i destroyed a psu that way.
Agree 100%. Be very careful when blowing out dust. And don't use the concentrator tube that comes with the canned air. Stay back about 8 inches from the fan (with the machine of and unplugged
) and do a series of short puffs rather than a long hard blast. Best to do it outside or someplace easy to clean since there may be a lot of dust in the unit.
Be careful not to breathe any of it in or get dust in your eyes while doing it. It's happened to all of us at least once.