As the title says I'm playing a multiplayer campaign with a friend of mine and for some reason there are black lines on his screen across the campaign map. His laptop runs the game better than mine and I have no such problems; the lines also aren't present in battles nor are they on water on the campaign map, just on land. He doesn't really mind it although I know he wants them gone - nobody wants giant black horiztonal lines on their screen when playing a game! Anyone ever heard of this before and know what to do to get rid of them? Thanks.

For reference, this is his laptop