My kitty Stix (1yr, neutered male) does the same thing to Kota (5mths intact female). When I first noticed him doing it, I saw he wasnt biting very hard at all and she would cry out loudly anyway, so I just raised my voice to them and seperated them. Kota would then run up to Stix and bite him on the rear when he wasnt looking!!! So I quit seperating them and let them fight it out. She is very vocal and growls for anything. They are not hurting each other as far as I can tell and they only do it for a few minutes at a time. Afterwards they end up sleeping next to each other like little angels. (yeah right!)