Hi, it is a Vertical line and yes it does drift slowly across the
screen.

I haven't tried unplugging the video connection from the sat yet, will
try that tonight, I have however tried to unplug the sat receiver power
cable and the problem does go away.

It's only really noticable during dark scenes of a movie (from the DVD
player).

What do you suggest?

The Monster website with their "Clean Power" add do mention the
vertical line problem... I'm thinking I might follow one of the
previous poster's suggestion and just buy, try it and return it if it
doesn't fix the problem.