I recently noticed her doing this at bedtime because my other Australorp tries to get underneath her on the roost to get away from the Orps that pick on her. But now she will be out free-ranging in the yard and will do it then. It sounds alot like the noise a broody makes when disturbed on her nest. I just can't figure out why she does it while walking around the yard. None of the other chickens are bugging her when she does it. Has anyone else experienced this? She is healthy, I'm just kind of wondering about this because it's a new behaviour for her.