Sounds like something my Ida does. She'll make this low pitched, almost a repetitious churrrrk sound as she just walks around. It can go on for a loooong time, too, and the only variation is the volume - sometimes she starts out quietly and then the volume just increases steadily.
She started doing this about a week before she got serious about laying. Now she does it every morning until she finally decides to go into the nest and get the job done. Then she sings her "egg song", Daphne pecks her on the head, and the whole process starts again the next day. Yours might be getting ready to lay, if she hasn't just started already.
