my guinea pig nipper is now 7 and a half years old and looks fine, but recently he has started making squeaks like he is in pain from his cage at random every 10 minutes or so. (he hasn't squeaked much for 2 years now). I noticed as I was feeding him that every few nibbles he had to stop and do some heavy breathing and would make some quite squeaks, he isn't smelling great and has a rumbly tummy aswell. I'm wondering if anyone knows what the problem could be. x