Pacer grinds his teeth when he's very excited--playing chase or waiting to go for a run. If nothing else has changed in Kaige's behavior, I wouldn't worry too much. If his teeth hurt, he'll change his eating habits so you'll know something's wrong. Since he seems to be doing it in a set pattern and you want him to stop, I'd break the pattern...give him a stuffed kong or some other toy to chew on at the time he usually starts to grind.