Screen flickering different brightness levels

[ExiLeZX]

Ok, I bought the parts and built myself a computer a few months ago. Ever since I got it, I've had a small problem. Every so often (at least once each time it is on), the display subtly flickers different brightnesses. When it does this, the size of the display also changes a pixel or two, moving back and forth with the brightness. Is this my video card or something else? I used the same monitor on my old comp and didn't have this problem.

I have a 6800GT PCI-E that uses a DVI-to-VGA adapter for my Viewsonic 19" flatscreen, if that helps any.

Its not a serious problem, but it gets annoying.

[Gizmo]

Have you installed the latest drivers for that videocard?

[ExiLeZX]

Yes. They've been updated several times, but the problem was there each time. Yes, I uninstalled previous drivers instead of writing over each time.

[peekaboo]

does this happen constantly?
can you make it happen by jerking the video cable?

[ExiLeZX]

No, it just randomly happens and lasts a minute or so. And nothing happens when I play with the cable.