@audphile1
Unpacking your username, I see you love AUD. So do I, but I just can't get enough!
Do I understand correctly that you have a WiFi mesh router about 1 metre from your system? And you claim it produces near zero RFI and EMI?
Surely the whole reason for having a mesh router is to blast the area with G-Hz WiFi signals?
When my partner moved her business into 'legacy' premises, wiring was going to be an issue so we (?) decided to go wireless for almost everything, including Voice over Internet Protocol (VoIP) phones. In the end, we needed two mesh routers to boost the WiFi coverage. These mesh routers get their packets via Ethernet cables. They also get their power over these same Ethernet cables, injected as it happens though little wall warts which no doubt have switched mode power supplies.
Always suspicious the phones might not be working properly, she would often dial her business from her VoIP phones, not realising the VoIP system was smart enough not to route the call externally! But then, a single unanswered call could cost her AUD 10k