Two things, hissing is in a sense vocalizing. So yes on this one.
Next, your king sounds(cause we can hear) like its nose was plugged up.
That said, we KNOW LITTLE TO NOTHING, about the hows, whys and what fors of snake comunication.
Things like the complexities of hissing or tail vibration and with our own rattlesnakes. Even such things as Large boas shaking their tails. We are VERY naive about these things and most of our thoughts are backed by rumor and theory.
In fact, a good percentage of biologists think snakes cannot hear. Even thought they have a highly developed inner ear.(depending on specie)
Me, I do not know what to think, most species that have a highly developed inner ear and make sounds, can hear. Most snake relatives do this. Lizards, crocs, torts, all hiss and make noise and hear. Snakes do all that and do not?????? I know, I know, I am thinking out loud.
Anyway, this subject should be subject to intense field study.
What I have realized over the decades in the field is, hissing, rattling and other noise making attempts do not foil their real predators, it sorta works on people. Sorta. Shovels trump rattles and fangs.
Their predators eat them anyway, and do not care if they are venomous or act like they are venomous or colored like they are venomous. They simply consume them. I know, more then you wanted to read.
So yes, keep questioning your snakes, watch the conditions that make them vocalize. See if there are patterns. Then post it here. Cheers