External 28' HannsG display slight flickering on dark grey desktop?

[ejosepha]

I have the macbook air revision C with the 9400 nvidia graphic card. I have attached external display with the mini display port to dvi adaptor. When I look at a full screen dark grey background, I see a slight flickering or jiggering on the screen. I know that this screen has a 3ms response time and with most colors I can't see this effect. But on dark grey or darker blue desktop I can see the waves or slight waviness moving behind the color.
Does anyone have suggestion? I don't see it on white, or lighter colors or even on black. Maybe it's wavy but less evident. Could this be the graphic card, the minidisplay port adaptor, or a fault in the screen. I can see that the computer does run somewhat hotter when in clamshell and running this larger screen, but the slight waviness or flickering I would like to solve, if possible.
thanks