As far as the hiss (?), an impending shed might explain that (most snakes want to lay low at that time & they seem to know before we do that it's coming);
also, they shed the outer linings of their nostrils when they shed, so sometimes noisy breathing goes away after they shed, or when it doesn't, sometimes
it's because the shed failed to come out of their nostrils, so it's something to take a close look at.

I asked about what you clean the cage with, just in case you were using diluted bleach, or something like that- it's both toxic & very irritating. (I'd want to
get out too, if that were the case...)

Cage temps: does he USE the hot side? does he stay on the "cool" side?