First the good news...it is possible the wheezing is a result of the pending shed...sometimes they can get skin inside their pits and it sounds like wheezing or whistling. Does he have any other signs of an RI? (head up, mucus around mouth?)

What are your temps and humidity? If these are good then I would lean toward the shed being the cause - if these are off then it could be an RI.

Personally I would keep a very close eye on him till his shed is over and if he is still wheezing take him to the vet.