Cooper's hawk, quite common in this area.
He or she was making the "cak-series" call, which is the second audio clip on the Audubon site; you can see its mouth wide open in pix 2, 3, and 4 (click on the photos to make them nice and large).
Gorgeous floofy bird pantaloons, yes? They look so soft and fluffy (unlike the awesome beak on this bird). Love!