Random 'flashes' on screen when playing game

[Hiram]

I was playing a game on a huge map today, only about 50 or so turns in, and I'm getting these random glitchy looking flashes on the screen. I've played on huge maps since I got the game and I've never had this problem before. It doesn't affect the gameplay but it's getting a little annoying. What could be causing them?

UPDATE: I restarted Civ V and resumed my game with no recurrence of these graphical glitches.