Computer Fan is really loud and annoying.

Any type of video? What does that mean?

Adobe Flash Player is CPU intensive, thus more power is needed to feed the CPU, which results in higher temperatures and often higher fan speed(s) on mobile computers. As more power is used due to Flash, the battery life of mobile computers is shortened by a good bit.
To check, if Adobe Flash Player is responsible for less battery time or the heat, go to Applications / Utilities / Activity Monitor and select to show ALL PROCESSES and sort by CPU.

There are a variety of Flash blockers for all the four major browsers available.
A Flash blocker does what it says, it blocks Flash content, but via a click on the marked Flash object, the Flash object can be activated and used.

• Safari: ClickToFlash, for which there is an extension and a plug-in; CTF allows you to download YouTube and other kinds of MPEG-4 encoded video too.
• Opera: has a built-in Flash blocker
• Firefox: Flashblock is an add-on to block Flash
• Chrome: FlashBlock is an extension to block Flash

Also make sure to have the latest Adobe Flash Player version running, you can get it here.​

 

Install iStat Pro to get accurate readings of your temps and fan speeds, among other things.

Performance Tips For Mac OS X

 

fan control

or try fan control. http://www.macupdate.com/app/mac/23049/smcfancontrol