Why does my PS3, Playstation 3, keep freezing?

I have 3 games, Lost Planet 2, Red Dead Redemption and Battlefied Bad Company 2 for my PS3. My PS3 has frozen at least once on all of these games. It is doing it a lot on Battlefield recently, and Battlefield is a pretty new game. It freezes everytime i try to find a Multiplayer game on the Kane and Lynch 2 demo. I take good care of my games and system, so idk what's wrong. It has done this since i got it last may, but only once in a while, now it's a common occurence, and Very annoying. I have it resting on the wrapping, plastic?, that it came covered in inside of the box becuase i also have it next to a chimney and i didn't want any dirt or anything to get on it. I don't have it wrapped up, it's just on top of the plastic. The chimney is never used, but all i can think of is: Bug in my PS3 (My friend's PS3 also froze a lot when i played it, so i thought it was just something that happened to PS3's every so often, once in a blue moon for mine because it was new); it is overheating, but i always check the heat of the system and try not to leave it on for very long; there is dust inside of it because the vent is facing the chimney, (in this case, how would i go about cleaning a PS3?) Please help, I'm getting preatty frustrated with this problem :/