Strange that it happens only at rendering. Does it do it when rendering in a different Window. It looks like a sync problem, but that would be strange. http://download.com.com/3000-2086-10018691.html This is a link to the Sandra program that will test and benchmark your system. It might help. It's a free evaluation. In the help file you will also see a link to a M$ patch for a registry cleaner. Maybe that might help. Sorry man. I've seen this before but it was a Vsync problem with the monitor and video card setting. I doubt that it's the case here. Hopefully others here might be able to help. Luck, Q

Un coup de dés jamais n'abolira le hazard
S Mallarmé