WTF is going on with my monitor?!?!?

For the past year or so, I've been experiencing episodes of strange visual artifacts on my 30" ACD (GeForce 6800 Ultra 256 MB). These episodes are very intermittent and disappear without warning. I'd describe them as bright green, single pixel threads running throughout the display, tending (but not always) to follow along the edges of color boundaries. Forcing a refresh by dragging a window or launching an application will usually make them disappear, though they usually disappear after a minute or two on their own (they disappear all at once, I believe). Tonight I managed to grab my camera and snap a few pictures (screen capture does not show them).

Sorry for the quality of the pics, but these should give an idea of what's going on. Is this a video card problem, an ACD problem, or something entirely different?

 

I actually have two monitors attached to this card: the ACD and a 17" NEC. The NEC isn't on all the time, though. I didn't even think to turn it on to see if it was exhibiting the same effect, and the effect only lasted a few minutes (as is typical). Darn.

The trouble is, it might be a month before I see this happen again. It's rather intermittent. That's the problem I'm facing: if I take it to the Apple store for diagnosis, they could run it for weeks and not see this happen, only to have it happen to me moments after I get it home. I can't seem to force it to happen.

I doubt they'll replace anything based solely on my hastily snapped pictures...

 

I'm pretty sure it's at factory defaults. I'm driving it at its native resolution. What other settings would be involved in restoring it to factory defaults?