Check out the enviornment first!
Hiya Timmeh!
Before you pack your snake up and take him or her to the vet, there are some steps to take in order to determine if your snake has an RTI or if it could be something else.
First off, how old is your snake and what is its routine habits and state of health? Has it ever had problems before? Does it eat regularly? How is your husbandry in terms of maintaining the enclosure and what type of substrate are you using? Also, how is the temperature variance in your snake's house?
From reading John Rossi's "What's Wrong with My Snake?" I have learned that there are environmental factors to be ruled out prior to diagnosing your snake with a respiratory illness. I was actually in touch with my vet and making preparations to bring my 8 year-old gravid female in when discussing this very issue. She was making clicking sounds, her throat was puffing up every 3rd or 4th breath, she was restless and rubbing her snout all over the place, among other things. I thought my maintenance skills were impeccable in that I changed her water daily, spot-cleaned when necessary, checked temps virtually all the time, and have her in a viv that is made of a nylon mesh which ensure proper ventilation. Upon closer examination, however, in addition to the fact that she was gravid and constantly burrowing and seeking a place for a nest in coconut fiber substrate, which has a very fine powdery texture when dry, I noticed that both of her nostrils were actually clogged! I even gave her a bath, as I was unable to get it out otherwise, but am unsure if this made it better or worse, because she kept clicking away! I was further appalled and even horrified when I caught her in the middle of laying her eggs that her mouth was agape as if she were gasping and it appeared for awhile that she actually stopped breathing!! (If you've ever seen a snake laying eggs you'll have noticed that "zombielike" state they get into, almost like they have that thousand-yard-stare! It's actually scary! And with her mouth open, well, it just didn't look right!). However, after she laid her eggs, and she drank a gallon of water, she did seem a lot better and the clicking sound was gone, but her throat was still puffing up. After her post-lay shed, which couldn't have occurred sooner, she was back to her old self!!
All of this to say that, while it MAY be an RTI, it MAY be something else. So while there are many unanswered questions, I would do a thorough check of your snake's environment first.
Will be looking for your response!!!