I was raised in So. Florida, and don't generally like snakes!
One evening, I was crawling through the bushes (don't ask!) and I think I got struck and probably not envenomated. It stung like someone had put a hot coal on my elbow, and I still have a dry, raw patch there, 60 years later. I crawled into my tent, and waited to die, but next morning, there I was!
I think the rattling thing is probably genetic, but some do and some don't.
Over the decades, generally, more of those that rattled got killed than the quiet ones. Now, more quiet ones have lived and procreated, so it is not as sure an indicator as it used to be!
I knew a guy who was hiking with a group of scouts in California, and several had crossed a log that was lying across in the trail. He stepped over it, and was hit behind the knee...no rattle.
Long, painful recovery. They all can be dangerous, so, like in Boxing...Protect yourself at all times!