Is this the pilot tone I've hard speak of? Is it possible to figure out what that tone is and notch it out as I've seen mentionedm
There is a 19Khz pilot tone for the stereo multiplexing so you are best off just low passing at 15 or even 10k. The tone is notched out but the notch filter only has so much depth. I can't imagine you having instruments with a large amount of 19k content either.
Depending on the age of the gear there are tone squelches on analog rigs. Again the tone is notched out by the RX. These tones vary my vendor. There are also "digital" tone coded squelches that work outside the audio passband to use a data sequence to secure the channel and provide a reliable squelch. These have nothing to do with digital modulation, it's digital data encoded analog, don't get too down in the weeds with the modulation types. Who is handling the RF out of curiosity (frequency coordination and the like)? Even though it is outside your parlance if nobody planned for RF coordination you may need to pick up the ball to keep from looking bad.