If your Mac’s fan seems to run constantly, is very very loud, and seems really hot, you should probably have it serviced. However, occasionally some Macs are afflicted with a loud fan noise for no apparent reason. The fan runs and runs very noisily, blowing cool air. This is most probably just a glitch and you may be able to fix it yourself quite easily.

To attempt this quick fix, shut the Mac down, and then unplug it from the wall AC power. If it is a Macbook with a removable battery, remove the battery. Wait five minutes and re-attached everything. If you’re lucky, the fan problem may now be fixed! If that does not work, you may need a firmware update from Apple in order to fix the problem. Go to this Apple page and see if they have an update for you.