I wanted to do an IFR flight on VATSIM with the Grand Duke by Black Square Simulations. While tuning the frequencies before departure, I noticed that I couldn't hear any ATC or other VATSIM audio through the aircraft's radios.

I'm using the free GTN750 mod from PMS50, but I also tried the other available instrument/radio configurations in the Grand Duke, and the issue was the same with all of them.

I've already checked and tried pretty much everything I could think of:

• Volume and squelch settings
• Different COM frequencies
• The headphone/speaker switch
• Different radio/instrument configurations
• vPilot audio input/output settings
• The "Monitor All" function on the iPad in the aircraft

Unfortunately, enabling Monitor All on the iPad didn't make any difference either.

The interesting part is that TX seems to work perfectly. ATC could understand me without any problems, so my transmissions were definitely reaching VATSIM. In vPilot, the correct frequencies were also shown and updated when I changed the frequency in the aircraft.

I also noticed that the TX indicator lights up when transmitting, and RX lights up when, for example, tuning an ATIS frequency. However, I still don't hear any audio.

To rule out an issue with MSFS or vPilot itself, I tried the Fenix A320 in the same MSFS 2020 setup, and the radios worked immediately there. So it seems to be something specific to the Grand Duke.

Another interesting detail: I do receive audio from the NAV radios. For example, when tuning a VOR, I can hear the VOR Morse/audio normally as well as any other aircraft sounds. So the aircraft's general radio audio seems to be working, it is just the VATSIM/COM receiver audio that isn't coming through.

Has anyone experienced something similar with the Grand Duke or knows if there is a specific setting I might be missing?

Any ideas would be greatly appreciated!