Got a reply by email from Dynon Support who say the Skyview HDX Audio output may be failing, the Audio Ground between the Skyview and Intercom may be bad or the Intercom itself may be faulty. According to another Support post (different problem) there is enough power in the Skyview Audio output...
My Dynon Skyview HDX was working fine and I have not made any changes to the software or wiring but the Audio Warning/caution volume suddenly decreased so that I can only hear the warnings when the Engine is stopped. The volume is low on both P1 and P2 Headset Jacks and with different Headsets...
