Regarding the sound recording shared by Rick Hollis yesterday, I concur that this is a Barred Owl noise. This is a very familiar sound to us, as Barred Owls breed in the woods behind our house every year. We hear this sort of call nearly every night through most of the summer. I always assumed it was the sound juveniles make when they are begging from the adults, as suggested by some other commenters. However, I am curious about it now as I recently read "The Homing Instinct" by biologist Bernd Heinrich in which he makes a somewhat passing comment that such a noise is produced by adult females. In any case, I'm confident we have a near consensus as to the species of bird, and the main mystery is solved. Incidentally, I've read several books by this author, and his excellent "Mind of the Raven" is one of the most fascinating books I've ever read about birds. I highly recommend it, as well as "Ravens in Winter", which is quite good.