Does this sound like R.I....?

[whoaxmary]

Alright, so just recently I've started to wonder if my pine snake Richard possibly has an R.I. He went through quarantine in a seperate part of the house, and I never notice anything expect a few weird poops. (He was fed eggs before I got him..) He was also kept in a basement with no light or heat, so I was almost expecting R.I. He is a very spunky character, he hisses costantly, and flicks his tail like he thinks he has a rattle. He never bites - and is slowly becoming better with handling. The past few times I've held him I can not tell if I am hearing him breathing, or if it's just a tiny hiss here and there?
He does not have any mucus near his eyes, or mouth, and seems otherwise healthy. . . I'm hoping it's nothing - but I should know better. Already have phoned the clinic to make an appointment to be save.