My son has a guinea pig that is 1 1/2 years old. A few months ago his back end started to roll around when he walks. My son took him to the vet who gave him sterioids and said if those didn't help he would need to take him to a specialist. We haven't been able to find any other information about why this would be happening. He seems fine in every other way. He is eating and drinking, however, he was very vocal before this started and now he doesn't make his noises very often anymore.