I once had a whistling snake. I took him to the vet, spent $150, went through many hassles. The whistling stopped after a couple weeks of medication, but to this day I still wonder if it was really worth it. I tried 2 medications. I had to change from the first one because whenever I gave him it he would produce TONNES of mucus and his nose would bubble. Anyway, just keep an eye open for mucus, or tilting his head and neck upwards, and other things like that.