Unfortunately the cable is molded in and I can't try a different one. If there was a short in the cable I would expect it to so up at all resolutions. I thought it might be possible that the cable was picking up radio noise from the PC. I tried to test for this by adjusting the VGA clock speed and/or memory speed with the thought that adjusting those would change the emitted radio frequency and the resolution or refresh rate at which this noise was observed would also change. But that didn't happen.
The little scan lines continued to only show up at 1600x1200 at refresh rates above 70Hz. So I suppose it could still be RF emitted from some other part of the computer, but I think having enough RF noise spill out of the case to affect the monitor like this must be against some regulations somewhere - so I kind of ruled that out.
This led me to think that the noise is coming from inside the PC circuitry since it can be clearly linked with computer activity. It's quite interesting actually, certain activities will repeatedly produce the same noise pattern. For instance, inside the Catalyst control panel clicking on certain items (though I don't remember exactly which ones, I'll have to check) will always produce a quick series of closely packed grouped lines that will move down the screen, it lasts about 1/2 second, then the system returns to more random lines zipping around. Other events have similar (but different) results. And most oddly, running the Freestone video stability test removes almost all the lines. It's weird.
This is a photo studio computer that is not usually hooked up to the internet, so I've been updating things manually, but I'll be able to get the machine online this Thursday so I'll check the AMD site to see if they come up with a newer video driver, or who knows maybe windows update will change something that will make this go away.
I'm going to attach a flat panel monitor to the board as well and see if I can make that do anything funky.
I'll keep you posted.
