I'm caring for a stray and she has an odd quirk. She growls ALOT. She isn't showing any signs of aggression or fear. She seems perfectly happy. She will growl even as she is rubbing against your leg or being petted. Her body posture does not indicate any kind of stress. She is very vocal in other ways as well, but the growling has me stumped. Anybody else experience this? Is it just a quirk?