Hi,
I had a similar problem with my Pro. Basically, the unit would work perfectly outside of the case, but once installed, sometimes it would be OK, sometimes the screen would be garbled with similar symptoms like yours.
First I thought that the contact between the LCD screen and the printed circuit board became loose, but after I checked and tightened everything I still had the problem occasionally. In the end I figured out that the problem occurs if I tighten the screws that actually hold the unit in the 5.25" bay to hard.
Try your unit outside of the case and/or check the connection between the LCD and the printed circuit board, maybe that helps.
Kind regards,
Boris.