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.