I agree, the chin is popcorning which is a sign of a very happy chinchilla. It is so funny to watch them do it, too. Another thing you will see them do is wall surfing. They will run straight for a wall or the side of the cage and jump, bouncing off of the wall, heading in the opposite direction.
Haha and i just got a chin wheel, but they dont seem to have any interest at all. My girl chin tried jumping on top and rolled off lol, so i was wondering if there was anyway for them to learn it?