my wife was driving me back from a job a few minutes ago, and we saw two grey colored 'planes' flying in formation at a pretty low altitude. they were not terribly big as far as i could tell, and there didn't seem to be anywhere for a pilot. they had propellers that could rotate, and they could hover. there were no visible markings on them. we were near the atlanta motor speedway in hampton, georgia when we saw them. there is a small airport behind the speedway, but i have never seen anything like this before. any clues what they could have been?