FPS Lag

For about a month now, my FPS has been lagging horribly. I'll play for a few minutes just like normal (30-40 FPS) and then suddenly it drops down to under 10 FPS for a minute or two, then goes back up to normal. This seems to repeat itself in cycles, and it increases the sticky walls glitch, crashes, and makes it impossible to play with consistency.

The number of players in a room doesn't seem to make a difference, and neither does smoke/spray/flashbangs, it just seems to happen spontaneously.

It is NOT my machine, which has above the recommended specs for CF, and Quake Live, Battlefield Heroes, Combat Arms, Counter-Strike, all play fine. It's a problem with Crossfire, and it needs to be fixed.