Can you hear him hissing as a rule, or just occasionally?
Anyway, if it's corelated with moves, may be nothing. There is a clear difference: "wet hiss" vs. "dry hiss". If wet, and also some liquid appears from the nostrils, may be a problem.
The less dangerous problem usually is a too... DRY atmosphere, that can irritate eyes and respiratory ways. I see it sometimes in my tortoises, when very hot and dry conditions occur.