Whistle noise while breathing (I don't think it's RI)

I've been noticing with my sub-adult and adult ball pythons, I will sometimes hear a whistle noise when they breath. I don't think it's RI infection because I've kept a close eye and I see no mucus or bubbles, I have checked the inside of the mouth and it looks ok as well. Again I only notice this on my larger ones, none of my smaller babies. Is this normal? I've read that it could be stuck shed, or water in the nose etc. However I don't think it's any of those things. Has anyone else experienced this with there bigger bp's? I have them in rack setups, 90 hot spot, humidity 50-60% (higher during shed).
Any input would be great.

Mine have done that a few times. If it doesn't go away in a few days I would take them to the vet. Mine has had water in her nose and she whistled for a few days.

I have a couple animals that are just whistley. They are not sick, don't have anything stuck in their nose, that is just how they are! My pewter male is the most noticeable.

Either its some stuck shed, some water, or that is just how their nasal passage is. As long as no other RI symptoms develop then they will be fine. Keep a close eye on them for mucous, bubbles, open mouth breathing, or popping/clicking noises.