I had this exact same issue with the Dittel FSG71 and the Zaon.

Sadly a ferrite core connected as close as possible to the Zaon did not solve the problem. I went so far as to put a choke on the power line to the Zaon with capacitors, and still had the issue. Ultimately, the only solution that worked was running the PCAS of batteries.

There is a screw on the side of the Dittle FSG71 that can be used to adjust the squelch threshold up or down. But this is not something you can adjust in flight.

Chris
42DJ