Well, gentlemen, I have the same problem with a Matrox G450 Dual Head 32MB:
The monitors I connect to it are flickering when I move the mouse around
the screen, or when a program runs. For instance, if I play a movie in
Media Player, the screen is flickering like hell. Now, this effect is more
visible on my monitor at home, which is pretty old and tired, but it also
happens on other monitors which I tested, to a lesser extent, but IT DOES
HAPPEN. At first I thought maybe it's about some bad contact at the video
connector, but it's not about that.
So, if someone could point out a clue in this nasty issue, I'd be
grateful to him / her

Thank you very much