Just to give you the run down. I recently purchased a different computer and in re-wiring everything, my monitor start to have fuzzy horizontal scrolling lines that would move slowly down the screen all the time. There were usually two on the screen at any given time and would takes several seconds to move to the bottom before another one would start at the top.
It seemed intermittent and I tried moving the cables around, but eventually it settled into being permanently there.
Anyhow, a friend of mine suggested that it could be interference as I was using the old VGA cable to connect to my computer. This is an analog signal and is subject to interference that digital cables are not. So I hooked up a DVI cable, since my video card also had that output on it and my monitor also had that input. That completely cleared up the problem and with the DVI cable I have none of those fuzzy lines moving down my screen.