I had a BR hen who did this - started crowing every morning. She and her sister were nasty little pullets who would swarm other hens and pull their feathers out, so they were put in their own special area adjacent to the main flock run. Finally they were trustworthy and I integrated them into the flock, which has multiple mature roosters - and the crowing stopped. It took a while to figure out which one it was crowing, but she finally did it right in front of me one day. Still laid eggs ... no physical changes.
