Asteroids Deluxe monitor problem?

[Evil Otto]

I have a deluxe asteroids machine with the following problem.  The game plays fine, but almost always after a game and when the high score entry screen appears, the top 1-2 inches of the screen start to jump and become distorted.  Once that screen leaves the problem is not as severe, but the top 1 inch of the screen (area where player score is displayed) bcomes off and on distorted.  Not sure if this is a monitor problem or not, but I figured I would start here first.  I can probably post a photo or two at some point if necessary.  ANyone have any thoughts as to the problem?
Thanks.