Angel is 7 months old and doing very well over all in the behavior department. However. . .occasionally when he goes in his crate (on his own) he will growl when someone either walks by or just moves! He bangs around like he's wrestling with something - sometimes there's nothing in there but his blankets. I usually ignore him or tell him "Ah ah". Does anyone have any ideas on what could be happening and/or how to stop him from doing it?