Becker AR4201 Radio Transmission Problem

Just purchased a used aircraft with a 5 year old Becker AR4201 radio that seems to work normally BUT no sound goes out on transmission. Previous owner says everything was fine prior to my purchase of the aircraft. No changes made. I am using the previous owner's Bose headsets. So I can understand the wiring was done correctly on initial installation.

The PTT click can be heard on the hand held radio opening the frequency, but no sound of the voice transmission is transmitted to the receiving handheld radio. Black triangle on top row shows the radio is transmitting. But no voice is coming through. Tried two different working headsets, one is a friends and is brand new. Same situation.

All functions on screen are normal. No error codes. Receives transmissions from the handheld radio and also receives the ATIS loud and clear.

What am I missing?

RMM