I am trying to identify a bird of prey.?

I was in my back yard the other day and saw three birds circling over head. They were birds of prey this I know but have never seen these before in my area(NC). I have studied birds of all kinds my whole life and am stumped by these. They were solid slate grey with a quarter of the wing white. The wings were rounded so this rules out a kite or a falcon. Most all falcon and kites have pointed wing tips. A common feature of a hawk is rounded wing tips. I only saw the bottom of bird. Voice was common of a bird of prey, loud with scratch. They could be an immature bird but three together was strange. I have looked through all 20 of my bird books, images on the net and have found nothing. I worked with a raptor center rehab and never saw a bird like this come through. I even raised hawks as a child so birds are not something new to me, well... this one is. If you can help please respond. This one is testing my ornithology skills.