From the sounds of it, this guy really has no idea what he is talking about.
If the snake has stuck eye caps, it is pretty likely that he has stuck shed in his nose that is causing the whistling.
There is no such thing as a "rhythmic hiss".
That guy is obviously not comfortable with snakes and is not qualified to diagnose problems.
I would find a new vet :/ Maybe quiz them with a few very easy ball python facts to see if they actually know what they are talking about. Like, ask the vet questions that you already know the answers too and see if he or she answers them right.