Loud noise! error 4mot/1/40000002:center_lower-front

My MacBook 2GHz Intel Core Duo has been making an extremely LOUD noise that seems to originate from beneath the top center of the keyboard. It sounds like an airplane motor! The laptop does tend to run quite warm, though this has always been the case since before the noise presented it's awful self. I assume there is something wrong with the fan? Everything else seems to be working normally.

I ran an apple hardware test and received error code 4MOT/1/40000002:center_lower-front

I do not have applecare - is it safe to assume installing a new fan might fix the problem? The help desk at apple quoted me $700 to open it, diagnose and fix the problem, but the purchase of a new fan is only about $50 on ifixit.

Any suggestions or insights would be greatly appreciated!

- Erin