Brand new imac with leopard and very loud fan constant noise.......

Without any more information than you have provided, the only thing I can think is is to shoot it or hit it with a rock.

More information please. You don't even show which model Mac you have.....

For the moment let's assume it is the fan. So the first thing to try is to reset the PRAM:

+"To reset PRAM, first shut down your computer. Turn the computer back on and immediately press and hold Command-Option-P-R until you hear the startup sound for the second time."+

and SMC as described here:

http://docs.info.apple.com/article.html?artnum=303319

Then I would delete the file:

Library/Preferences/SystemConfiguration/com.apple.PowerManagement.plist

and reboot the computer again. Post back if that does not work....

Yes...alt/option same thing. But since windoze calls the option key the alt key and since there are now so many ex windoze users using Macs, Apple decided in their wisdom, to add the "alt" to the top of the option key.

No caps! It's already hard enough to hold down the option, command ("Apple key") p and r without having to throw in the shift key! You have to hold the four keys down while at the same time hitting the power button and hold them (just the keys, not the power button!) until you hear the second boot chime. Then release the keys and the Mac will boot normally. After you have done this a few times you will be ready for piano playing! It's very awkward, most likely so that one cannot do this accidently.

Hello

I have the same problem i did resets but i cant find it the file to delete.
Please help me if you can.

I also had the same problem on my new Macbook. i reset the SMC and restarted the computer. I could not find any such file to delete at that location. however, the noise had stopped after resetting. Thanx a lot.