Tear Issue

I've got this recurring issue with my published screencasts. At some random points for a few seconds, a large part of the screen will disappear or tear (as shown below)

This page pictured above is  correct and what it should look like, but the very next frame looks like what is pictured below. That lasts for about 4 seconds and goes back to normal. This happens on and off throughout the screencast.

Any help at all would be greatly appreciated, thanks!