I've recently had very, very, very extensive experience with this loud tone problem with the radios. I've narrowed it down a little. When only one radio is on, it doesn't seem to happen. It sounds like someone is standing way too close to their amp / speakers while playing electric guitar...and they refuse...to..step..away.
I can't help but feel like it has something to do with radio encryption or freqs getting crossed somehow, or one freq accidentally trying to be used by two things at once. I bet that would recreate the sound, for someone not already suffering it.
But then I also can't get ahold of the units that I know I set to the freq I'm set to on Radio1 while Radio2 is off. It seems one radio at a time is the only way to keep it from making the noise, but the AFAC is grey'd out and I can't reach them.
I'm going to try changing the easy-comm setting and see what that changes. I sure hope that isn't what is causing the problem. I could've used regular comms so long ago, easy was just convenient while practicing other systems and custom missions while taking note that everything displayed the correct freq while playing.
Now that I've finally found a few people who maybe understand the problem, I'll definitely be checking back in, especially if I make some progress.
EDIT:
So, since I was worried I had redacted and adjusted too many aspects of the mission I'd been working on all evening for it to begin working correctly, even if I did find the problem, I started over with a new mission, and gave things legitimate frequencies to use, and turned off easy comms. It worked perfectly!
I started over creating my custom mission because I tried using that "pre-settings" thing, I forget what its actually called, where you hop in the plane and set it up for the player beforehand, jump out and back into the MissionEditor and save the mission. Anyway, I was worried something I'd done in that may've been attributed to the problem. So I started fresh. If anyone passing through knows how to "undo" a pre-configuration through that aspect of the mission editor, please lemme know. Its kind of inconvenient if to remove presettings, you have to just totally redo the entire mission. It was quite a complex mission with lots of triggers, zones, paths, pictures, descriptions, radio messages, radio message timers adjusted correctly, and enemy / friendly AI waypoint ETA timing matched up perfectly how I needed it, to cause the fight that I wanted. =(
Hopefully I don't get that far again and realize I can't remove something I thought would make playing it more intuitive.