Help. My six year old male normal has this hissing noise (not a whilstle) coming out when he breathes but his mouth is not open. I see no other signs of illness, no mucos, no bubbles, no open mouth breathing - what could this mean??

I just noticed it for the first time this morning - should I rush him off to the vet?? Should I isolate him from the others??

Please, if someone could help out.

Thank you.