How do you tell if a snake has a RI?

I've heard what sounded like sneezing coming from the snake's enclosure last week, and a few times before. I haven't seen any mucus around the snake's mouth. The tongue is still forked when "sniffing" the air. No dried mucus on the mouth or anywhere in the enclosure. I haven't heard anything since last week.

I've read that snake sometimes pass gas. But the sounds I heard seemed to be a forceful burst of air. I added an UTH to the CHE i have already cuz the temps seemed a lil low. Hot side now high 80's, cool side low-mid 70's. Humidity usually around 50%. The substrate is repti-bark, which i noticed can become dusty when dry. Could this be the culprit?

Can a RI clear up on its own? Do signs of a RI come and go through out the course of the infection?

The BP is one year old, eats 1 small f/t rat every week, and otherwise seems healthy.