Foxy does this.

She will growl when you play tug of war, but she will also run around like a completel maniac and growl at you. Even if you aren't playing. You could just be walking from the living room to the bathroom and she'd run after you barking and growling alot... at first I didn't know whether it was play or what. I do think with Foxy it may have been a dominance thing with me lol.

Saying that, Foxy growled alot. Pretty much most of the time. She'd growl at everything and anything to be honest.