Do you have SH3Commander? I belive you can adjust the t/c for that plus much more of course in commanders options. Someone will be along shortly to confirm.
I have approximatly 2000 radio messages plus tons of jazz WAC tosses at me through contact / task force reports. I happen to like them alot for game emersion. Plus a custom msg received ogg.
But to each their own. Sounds like you would be ok with getting the message as long as your t/c isn't dropped to 1. It's not like the player has to got to "M".
