Screen distortion

Hi

I have a 1 1/2 yr old mac pro and over the past few months the screen does an odd thing. It has only happened 4-5 times in total and is completely random. Essentially I will be woking away and I can open anything (word or internet etc.) and suddenly the entire screen becomes slightly fuzzy as if there are two images of everything on the screen superimposed but somewhat off centre i.e. one on top of the other but not perfectly overlaid. I guess what I'm trying to say is there a ghosting type shadow and the colours appear weaker and hazy.

This appearance will stay for as long as the machine remains on. If I reboot then everything returns to normal. It is so intermittent that I know if I take it to Apple they won't see anything. Anybody have a clue what is going on here and what I can do about it?

Also what is Apple's replacement policy on a machine like this (still under warranty)? The reason I ask is that since owning it from new I had a sceen flicker problem which resulted in the display monitor being replaced, the problem returned 2days later and the machine was taken by Apple for diagnostic bench testing for 48hours - which it passed. The flickering problem returned a few days later and was then witnessed by the Apple genius bar and went in for a graphics card replacement - this was all in year one! Now I have this current intermittent problem.

Regards

Jawad