|Barred Owl. Photo courtesy of USFWS.|
The Cornell Lab All About Birds page refers to this raucous behaviour as "Pair Caterwauling" and says "During courtship, mated pairs perform a riotous duet of cackles, hoots, caws and gurgles." You can listen to a subdued version here: http://www.allaboutbirds.org/guide/Barred_Owl/sounds
Our neighbourhood owls were much noisier!!