Horizontal lines during intense gameplay

Hi all,

Here are my specs.

Ultra 500 Watt Power supply+Visiontek 450 Juice box power supply in addition to my other power supply
XFX nforce 750i Motherboard with sli capabilities

two XFX 9800gt Video Cards in SLI


I was trying out call of duty 4 for the first time today and noticed that during the first sequence of the game The real intense exit of the ship where it is flooding and you have to run out to the helicopter (playing at 1080p with 60refresh rate) the the screen cut into a few horizontal line breaks on the screen-everything seems to run okay, but it is really annoying-

ive noticed it do this during some other intense action, like the respawn screen during borderlands etc.

CAN SOMEONE TELL ME WHAT IS GOING ON?

Thanks