Heavy Breathing

Question
I just bought my baby rat Baley from Petsmart two days ago. At the store he was running around and investigating, and he looked fine. But now that he is home, he has mostly been sitting in one corner of his cage (wire with plastic bottom and recycled paper bedding) breathing rapidly and heavily whenever I go near the cage. I have seen him looking around a little bit, but not much. He doesn't run away when I try to pick him up and he seems to like being held for the most part. And last night he was making this sound that sounded like the noise a guinea pig makes when it is happy. I was just wondering if this was all normal or if the breathing was something to worry about?

Answer
I'd worry about it. Most likely he has a little stress cold (that is literally as it sounds - a cold brought on by stress). Watch him for a few days and see if it subsides on its own. If it gets worse, take him in immediately. If there's no change, I'd think about getting him to a vet, because respiratory problems usually get worse.