Yeah, this sounds like a fan issue. My old computer did the same thing with the two fans on the mother board! I opened it up and found one of the fans was starting to seize/grind and that's what was making the noise. I replaced the bad one but should have replaced both.

Eventually, the other started to have the same problem and eventually the board gave up and died.
Now, which fan exactly it is you'll only know by opening it up and watching it run... or take it to a pro. Fans are pretty in expensive and even
I was able to replace my own! I would definately address this issue and soon! The fans are intended to keep parts cool and when they're not working things start to "fry." :eek:
Let us know what you find out!
ED