Fallout 3 skips ~20 frames periodically

Hi guys..I'm runnin fallout3(1.6update) on my comp and I get average 80fps, the problem is that every so often I will turn the mouse and I will notice a skip...sometimes even freezing up the game, I tried defragging, have no antivirus s.ware, and no internet hookup so I don't think its a virus...any ideas? Here's my build : i7 920, env gtx285, 6gb gskill, 2 WD 160gb s in raid0 (OS), msi x58 platinum sli mobo... o and I overclocked i7 to 3.5ghz stock fan, gtx285 to 710 core freq.