My screen periodically starts flashing and getting huge white lines that run down the screen when I play games (only have crysis maximum edition) but then it stops and goes back to normal. Ive noticed that it doesnt happen all the time, and not at certain moments in the game (i.e. happens at one point but doesnt happen again at that same point a different time) and it will stop if i go and look only at a wall. Is this normal or is my MBP F'd?