Monitor Jumping

I have a Mac Cinema Display A1038 monitor connected to my PC through the DVI to ADC converter, and I frequently experience screen flicker, where the image rapidly jumps down about a quarter inch, especially during loading screens and while watching videos. Interestingly enough, if I alt+tab during a loading screen that causes the flicker to another window that is full screen, the flicker still occurs while the loading screen is in the background.

My PC is a stock HP A6620F with a Radeon HD 4850 video card and BFG ATX12V 2.2 550W PSU. I have the latest drivers for the video card. I tried connecting my computer to a different monitor (for which the converter is NOT needed) and there is no flicker on the other monitor. I’ve also tried connecting the monitor to a different computer (for which the converter IS needed) and the monitor does not flicker. So, it seems neither the monitor, the converter, nor the computer is the issue. I have run completely out of ideas. My friend suggested getting a decent surge protector, but I doubt that will have any effect as all my tests stated above I used the same power strip. Any suggestions on how to fix this would be greatly appreciated as the flicker makes doing most things annoying and others impossible.

Is it possible this problem is caused by the sync rate of either the monitor or the video card? I'm racking my brain and the internet and I am no closer to a solution. I'm willing to try anything at this point.