MOrning! I've just been out to fill the feeders for my lot and when I stuck my head into the nest boxes noticed that another hen had tried to take a peek into an occupied box, the hen trying to lay let out a sort of squealy noise, several times that could have sounded like pain but she seemed to be saying "oi, back off this is MINE!"!"
thought of you at the time and wondered if it could have been similar?