Chinchilla laying on side against cage?

I've had my chinchilla for five months now, and this has been going on for a long time now and it's starting to get concerning, whenever he returns to his cage after playtime he lays against the cage on his side? I heard this can be because he's too hot, but the temperature never seems to go over 72? Although my door is always shut due to cats, so it might get a little warmer in there so whenever I think it's warm in the winter/fall I open up the window to let in some cool air, but he still lays there? I think he might just to that because he wants to be let back out, but I don't want to assume since it's worrying.