How are you measuring his temps? He might be too hot, especially if you're readings are off a few degrees.
Is he possibly going into shed? that can bring up a hiss or two. Do you hear this "wheezy" breathing when he is laying flat & NOT
being held? When we hold a snake it can force air from their lungs is such a way as to sound like a wheeze issue, but may not be.
What have you been cleaning his cage with? it's possible that the residue is irritating his lungs.