Could be the fan also. This on games or just when you go to facebook? Listen from where the sound is coming from. Is the sound normal or grinding in any way?
Check where the sound is coming from. If you play Facebook games, but no other games, your computer could just be working harder to process the game data and speeding up the fans to keep cool. If your hard-drive is the one that spins up every time on Facebook, do a virus and malware scan. Good instructions are on the sticky post on the forum. http://www.tomshardware.com/forum/242796-44-simple-free-guide-removing-malware