M15x Performance problems

I bought my computer about a year and a half ago in the summer of 2010

Hopefully someone can help me, I've been having this problem for close to 3 months now.

I'll start gaming, and after perhaps 15-20 minutes, I'll suddenly get a major FPS drop and my games become all laggy. Also, I briefly hear a sharp, well....buzzing noise that lasts like half a millisecond, and happens just before the performance drop, like the system is lowering performance. Thing is, I've already tried setting the fans to active but it made no difference. Also, no matter what the setting of a game is (low, medium, high, very high) the performance drop will remain the same and the game will still lag. But, after maybe 30seconds to 1 minute, the performance will pick back up, returning to normal levels and no lag problems. Wait another 3-5mins, and the same thing will happen, then 30 or so secs later, itll pick back up again. This goes ON AND ON AND ON AND ON. I am convinced that theres a problem with either the video card or cooling system, but I wanted to put a post on here before I called like Geek Squad or something. Also, when I can hear the fans running but when I put my hand near it I dont feel much air, if any, coming out. Thats a problem, right?

Settings:

Intel(R) Core i7 CPU @ 2.67 gHZ   2.66gHz  (turbo can get it to 3.3gHz, but I dont really know how to use it..)

Windows 7 64-bit

8GB RAM

Nvidia GeForce GTX 260M

Core temps average between 51 and 55C