Ryan,
I can almost guarantee you 100% that it had nothing to do with the TV Show.
I can imagine you have already thought of this, but someone went to a lot of trouble to first find your phone number. They then spent thirty or forty bucks and bought a disposable phone. They called you and threatened your life. They probably threw the phone away after that.
Does that sound like a kook, or someone from a forum just pulling a prank? NO. Do not take that threat lightly. Be very careful. Remember how I posted previously that I never broadcast my comings and goings into the Supers? Now you know why. If someone thinks you may have a chance to find what they have been trying to find for many years, there is a better than average chance (if they know when and where you are going to be) they may wait for you out there and take potshots at you. There have been a lot of mysterious (and also a lot of not so mysterious) deaths out there. Don't put yourself in a position to be the next one.
Take Care - Mike
...After hearing this, it kind of makes me feel unsafe now going out there. You really think someone would be out there waiting? I just assume most threats are not worth a crap and are hollow. I just don't like bullies or people telling you what you can and can not do. It's a free country. Ryan (or anyone) has every right to go out there on public land and do his videos. But as someone else said (I think Frank), don't broadcast and go with a group of people with the proper equipment. But safety is key.