Fans are on a lot.

The Apple Certified Tech's answer above is a good one, and maybe the correct one. An additional solution for me has been to download SMC Fan Control, a free add-on that will allow you to manually (or automatically) control the fan speed, and in additional will show you the temperature in your laptop.

http://www.macupdate.com/info.php/id/230...

In my experience as an Apple Certified Tech. this is usually due to SMC firmware needing to be upgraded. You can go to the following link and download the update: http://support.apple.com/kb/DL350

Also, check the exhaust ports for debris and lint - use some compressed air to try and remove it.

This problem occurs with a lot of notebooks. The cooling module attached to the processor gets clogged with fine dust and lint. The processor heats up quicker and the system turns the fans on high speed a lot more often and for a longer period of time. You should open up the computer and blow it out from the inside back through the air outlet. Otherwise you will be blowing the dust back into the computer. If it is clogged you will get a pretty big cloud of dust so do it somewhere where you wont get yelled at.

you might want to look into a program called "Chud Tools" they include somthing called "Nap" mode, in earlier operating systems. in snow leopard, or leopard, and tiger, there should be the option to turn on nap mode already there under the "hardware" tab in system preferences, then simpily, turn it on, this should resolve the fan issue. Noise was a big problem in late model powermac g4's and the CHUD tools were a lifesaver to people whose g4's were ridiculously loud.

It usually means that your computer is running too hot. I have found most laptop do not cool adequately and need extra cooling. I suggest that you buy an external Fan that is made to sit under your laptop and plugs into the USB.

This is cheaper than a new laptop, as the extreame heat will cause the processor to fail.

This happened to my MacBook when I first got it and migrated from my old MacBook. After putting up with the fan for a while, I opened up Activity Monitor and discovered an old startup item that was going out of control. Deleting that calmed things down. I usually look for a software cause before assuming hardware is the culprit.