I had something like this happen before with one of my pythons when a piece of skin became stuck in her nose. I put her in a large clear plastic storage container with warm damp paper towels and let her sit in there for about 15 to 20 minutes for ensure the dry skin in her nostril had become wet enough for removal. I used a children's oral medical syringe shown in this link that I carefully placed over her nostril and pulled the syringe tab very carefully till I saw the flap of shed stuck in her nostril come out (forewarning with doing this, they will squirm a ton and you need to be extra careful when pulling on the syringe and not to cause any damage). After that I used a pair of regular tweezers and gently pulled the skin away from the nostril, and POOF! Both the leftover skin and constant whistle were gone. I'm not saying this is a sure fire way to remove it, but I've found it's worked for me the best with shed skin the nostrils situation. Hope this may have helped!