1) Uninstall Fan Control app (maybe you or some previous user has installed it on your system):
Please follow these instructions to uninstall FanControl permanently:
- Remove the following files and folders (both on your start disk):
(You will be prompted for the Administrator's password when deleting these items.)
- Reset the System Management Controller (SMC). Please follow these links for instructions: Portables, Mac Mini, Mac Pro
2) To repeat the last step of the first step - reset SMC. Before starting your MacBook Pro, hold left shift, control, option and power key at the same time for a few seconds and release them at the same time. Then turn your MacBook Pro on.
3) If you have installed smcFanControl, then reinstall it.
4) If the fans are still loud while CPU load is low, then you have to probably open the bottom case and clean the fans manually.
These instructions worked for me on my MacBook Pro (8.2 15" Early 2011 with OS X Mountain Lion 10.8.3) after cleaning my fans twice and few hours of surfing for the help.