I'm sorry I didn't realize this post was that old, I'm new to the site. But no he doesn't hold open his mouth, everything else is normal. He eats, drinks, acts just like he normally does.
My chameleon is about 4-5 months and is also making the wheezing sound, he only seems to make it when he's being handled. However he doesn't like to be upside down lol. I just began to notice this a week or two ago. Did your chameleon have an infection?