What do I do?

[CloudtheBoa]

Hopefully there's nothing wrong with him! Retics, especially as they get bigger, just get noisy. If there's no mucus or anything, an RI is not very likely.

My SO has a bullsnake (I believe), and he can be a pusher. His face healed cleanly except the nares are nearly completely closed, but he often sleeps with his mouth wide open and will randomly let out a loud whistling sound that could be mistaken as an RI. So if your retic is a pusher and has damaged his face, that could certainly be another cause. As mentioned, larger enclosures can help, as well as adding some hides and things to climb around in/hide behind.