In the Smokies at high elevation, two birds buzzed the tree tops at high speed creating a sonic blast. I'd never heard anything like it. Thought that it might have been a falcon or something. I had no idea what I had witnessed, but now I know.... it was the dive of the Nighthawk.
Listen at the 18 sec mark of this video. It was actually pretty frightening. Privileged to have seen and heard it. Twice.