It might also be worth pointing out that s small piece of loose or stuck shed in the nostril will cause a squeaking/whistling noise. I would not be surprised if the noise goes away with the next shed. If the noise persists, or you notice other RI symptoms then you should see a vet. Even if it is an RI, it is its very early stages. If you are looking out for it and treat it quickly it shouldn't become a problem.