Vertical lines on monitors

Over the past few weeks, I have noticed that I periodically have faint vertical lines a fraction of an inch wide and a few inches high on either of my dual monitors being fed by an ATC 9800 Pro video card.These lines are very intermittent, do not show up in the same place each time they appear, and can be on either of my dual monitors but not both at the same time. They also can appear in multiple positions. For example, with a Word program up on my secondary monitor, I see 5 green lines at random height and positions. I closed the Word program and the lines are gone. When they appear, I can also open any other window and move it across the screen in question and the lines will disappear,These lines are not intense enough to really interfere with displays, but are just faintly present, and as mentioned above can be easily removed for the moment at least. They appear on the desktop, word, excel and when other such program displays. Now the kicker. I have NEVER noticed them on an FS9 display.Sometime back, I discovered that my fan was not running on my video card. I got it started and have not caught it locked up again, but I fear that the problem may result from past overheating on this board. I tried various drivers and still periodically see the lines. I guess it is time to drag out an older video card and see if they appear with it, thought possibly someone else had been down this road.I have a third monitor running off of an AGP port and have never seen the lines on that monitor. Anyone else seen this happen and/or have any suggestions?RTH