I just developed the same problem this week and was about to ditch it and buy a clone. Thanks for the tip about shining a flash light into the screen. I see what you mean.
I described the problem to my favorite computer repair shop and they understood the problem and will take a look at it. They never heard of a Cintiq but they knew the problem as it applies to monitors and had a few suggestions to check. I will let you know what they do, if they can fix it. Have you already had your fixed and know the solution?
Hopefully it won't cost $880 like Wacom's flat fee. I don't know how I will carry this 24" cintiq though.