Hmm... interesting. I have exactly the same problem with my Voodoo- card. The vertical lines are spot on....
Began a while ago when I started to fiddle with the hardware. After adding Indivision MK-II, ZoRam and a FastATA board. Also made some attempt to replace the Voodoo card with a Radeon, but that never worked out so I replaced the voodoo card again. It all happened with some holiday in between so I cant exactly remember when they started to appear.
What Ive seen is that they dont always appear, and when they do, it seems to affect bright colours less. Hi-, or low res don't seem to matter, they turn up on both maxed out WB- screens as well as low res Quake screens. Very strange.
