Pastel Problems

Ok so I am having issues with my Pastel. I worry because he is my First snake and is normally very nice and I have never even heard him hiss before yesterday.
Here is the situation:
About a month ago I had all my snakes on Aspen bedding and noticed it was VERY dusty after about a week or so. Changed to Repti-Bark now (love that stuff) But while on the aspen I noticed that he was breathing hard. Like I could hear him exhale heavily (well heavy to me because I normally don't hear them breathing).
I have been constantly checking him for an RI but nothing shows up. No mucus no nothing. Temps are spot on (on a Ranco and just bought a Herpstat Pro for the collection, incubator and babies) and humidity is around 45-60%.
Yesterday I was "petting" him while I took him out and he make a heavy exhale and/or hiss but no striking position or anything and what not. So I checked him out closely and still no mucus or bubbles. Opened his mouth and it look normal and fine (color was a like pink to white color). He doesn't make any popping sounds and has been eating. Has it just got grumpy with age?

Balls will hiss when they don't want you messing with them. I have two females that do it on a regular basis. Neither shows aggression, just lets out a loud hiss and then gives in lol. I'd say he's just being a little grumpy from what you explained.

Yea he did just give in. haha But it's strange because I have had him over a year now since he was a month old and he has never done this. NOW my fire is a grumpy butt and love to bite me every chance he gets, but I find it cute because he is small (compared to me).
But yea this whole RI thing was throwing me for a loop. My husbandry is perfect, maybe alittle lower humidity (45%) in some tubs but nothing lower than that. And my snakes never see any temps below 79.