The pilot tone is a high frequency tone (outside of the audible range) which is modulated onto the RF signal from the transmitter.
When the pilot tone function is switched on at the receiver menu, if the receiver does not detect the pilot tone, then the receiver will stay muted (even if it has a strong RF signal above the squelch threshold).
Pilot tone is an additional safety against interference on your frequency when your transmitter is out of range or turned off.
Change the "PILOT" tone setting in "ADVANCED" menu
note - pilot tone was not used on the original evolution wireless series (only on G2, G3 and G4) - so if you have an older transmitter which you are using with a newer receiver, you will need to turn pilot tone off at the receiver