Black bird with white underwing with black border
I am in upstate South Carolina. In late October on four different occasions, I saw a stout all black bird flying fast in a straight line, not too high, wing action like a duck, emitting harsh squawks rapid fire in even tone. It was flying from wooded area with a small river. It impressed me as a water related bird, It was about crow size, but fuller bodied. Here is the kicker - its underwing was white with a black border evenly all around. I can find nothing like it. Some have suggested pileated woodpecker, but it did not have that head, no other markings, and pileateds' white underwing goes all the way to the front wing edge with no black border. I'm sure this bird must have been migrating through our area. Any ideas?