iMac Fan very loud

Hi there!

I have an iMac (2008ish), running 10.6.8

Anyway, the fan on the iMac will speed up, to a point where you can hear it very well (and it gets very annoying), after the dock shows up (Not right on startup)

I took it to the apple store, and they ran diagnostics, but said they couldn't fix anything argh...

The CPU fan is running at 3900 rpm, which I believe is extremely abnormal, considering the only programs I use are firefox, and mail.app

I have reinstalled the OS, and there are no files that could be the problem

Does anybody know of any solutions? I have tried multiple fan control apps (smc, fan control, etc.), but none of them let you control the MAX the fan speed is (as that is the problem!)

Any help/app suggestions you could provide would be fantastic!

Thanks a lot!

Grant

If it were mine, I would start with blowing out the vents at the bottom of the unit with some compressed air. After awhile, the ducts will start to get caked with dust, making the fans work harder than they need to in order to move air.

Barring that, I would disassemble the machine and give it a more thorough cleaning. And if that doesn't do the trick, I'd be changing the fan(s) out. At 3900rpm, they shouldn't be all that loud.