Thanks for the ideas. Even though I am an EE with 25 years of experience, still doesn't mean I want to run a new phone line from the basement to the second floor through finished walls!

My latest update is I got three days of clean calls with the two wired phones, then I added the DECT back in and coincidentally or not, started getting the pulsing again. It is not 60Hz. I had the pulsing during a call and ripped out the DECT during the call, but the pulsing did NOT go away. So my coincidence and theory kind of got shot there. I replaced the DSL filter on the DECT phone with a new one, long shot but something else to try.

Outside of this, I have a ticket with Voipo to see if they can send me a different ATA, Grandstream or otherwise, to see if it is directly related to my specific box.

I can't rewire the house. Not when I had almost 2 years of voip service with a Linksys box and same DECT and same wiring without any issues.