After months of putting up with static and noise on the audio, and several efforts to troubleshoot the source(s) the culprit may have been a defective Dynon SV-Intercom unit. A replacement unit was received this afternoon and passed the bench test before being installed in the panel.
Symptoms: 1) Power Light - flickered with audio activity but didn't stay ON once the Squelch level was established. 2) Co-pilot MIC - worked with Squelch set at ZERO or slightly above that, but cut-out 100% of the audio above that level. No volume of shouting would activate MIC. 3) Co-pilot MIC - once 'cut-out' (#2) the intercom was dead until power was cycled. 4) Co-pilot PTT did work as long as (#2 condition) had not been triggered. 5) Co-pilot - With no MIC plugged in to jack the wiring harness was probably acting as an antenna and amplifying any and all interference to the Pilot phones (and GoPro plugged into the Co-pilot phones).
New unit exhibits none of the above bad symptoms and seems to be perfectly clear. This problem was largely allowed to persist during Phase 1, with the thinking that it was not relevant to Solo flight ops. Should have been addressed. Dynon support was excellent.
