That is definitely concerning, but it could have to do with shed. Snakes often yawn to loosen up the skin on their face prior to shedding, and this may cause excess saliva to build up, possibly making slight wheezing sounds. Loose skin in the nasal cavity can also make a wheezing sound when they breathe.

Hopefully the mouth opening / sounds won't persist after he sheds, but if so... Could certainly be a respiratory issue.