I'm having the same issue as you, the only diffirence is that I'm using GTX260 Graphic Card and that I don't get any artifacts. But the Freezes are realy P!ssing me off.
I advise you to go to Activisions Website and mail them about this problem, I did the exact same thing today. Once I get a useful answer from them, I'm letting you know.
Gl!
P.S. I've been having these freezes ever since I bought my PC, and thats about 3months now
