Dumb question: did you turn up the volume for the one you canít hear? Iím sure you have but didnít see that in your description. If so then check the pins between the two units and make sure they arenít backwards or one off and good connectivity.
Ser 140142, RV-14A flying - N1463
Ser 83825, RV-8 building - N8638?
USN Ret, Urologist, AME, Repeat Offender