mines had the same "problem".
your temperatures seem about right.
when was the last time it shed? sometimes the whistling sound will occur pre-shed. It happened to mine.

Check for bubbles or mucus on the nose area or in the mouth and gums. if there isn't any, then chances are it's not an RI. BPElizabeth (a very knowledgeable member of this site) suggested using a cue tip to open the mouth and check for bubbles or mucus. you might wanna be careful though...they're not too partial to that...

still keep a close eye on it and if you do notice mucus or bubbles, take it to a vet...