hehe, thats what i was thinking of when I read it.
Yeah, there should be something in the game options about it too, since its more likely it'll be on on there and not set to always on, in the video card settings, or I think even in 3dmark, it'd probably override the settings and turn it on too.
Check both, and hopefully the problem will be fixed.
If you get this weird flickering effect though, called banding I think, it'll be because the video card is rendering faster than the monitor is set to display at, and the monitor when it is ready, displays the next frame, which is why you might get this when moving about fast. Some games get it more than others, and so if you have a fast machine, it is best sometimes, to turn it on.
This is because, if you think about it, what is the point getting 300fps, when only 60 is displayed anyway?