If he is about to shed or just shed, sometimes they get a bit of shed stuck in their nostrils and that can cause whistles and other odd sounds. Sometimes a hiss can sound like a wheeze. So it might be nothing at all to be concerned about.

What I recommend is that you hold him near your ear and listen closely to his breathing for a few minutes. If it is an RI you'll likely hear an assortment of pops and whistly/wheezy sounds, although if it is a mild/just starting one, they may be faint and far between. If you don't hear that, then just keep a really close eye/ear on him to be sure, but you are probably fine.

One other thing to do is to get a look in his mouth. You can gently open it using a qtip. If you see an obvious puddle of mucus, that's a bad sign. They do have saliva (or at least something wet in their mouths, dunno if it is technically saliva) though, so a very small amount is ok.