I sometimes get whistling noises out of my nose too. It doesn't mean I have an RI. This usually happens when I'm breathing hard and it's quite dry. I'll get a piece of dried snot stuck in my nose narrowing the nasal passages and causing hard forceful breathing through my nose to make a whistling noise. Usually a good hot steamy shower or a session with the neti pot will take care of the problem for me. For your snake you might want to try raising the temperatures and the humidity. Try a plastic shoe box with a hole cut in the side, stuffed with damp sphagnum moss and placed on top of the heat source. Some nice warm humidity could do wonders for your snake.
Then again, maybe he just doesn't know the words to the song...