Ive been having a similar problem...
When i play call of duty 4, ill shoot the ak 47 and my screen goes crazy into like horizontal breaks.
I turn vsync on and it works sometimes too.
My problem is that i am also trying to sli 2 xfx9800gt cards
See if this is what your problem sounds like:http://www.tomshardware.com/forum/286449-33-friendly-9800gt#bas