Just had to let you know. With the manual "re-digested" I plugged the testerlinc back in again...wasn't terribly concerned with line noise, which had been at or near zero when I briefly used the testerlinc la st week. Today though I was seeing considerable line noise.
There was not a lot turned on so to start I started turning off switchable devices.
It wasn't long that I approached a little used reading light. When I turned off the line noise disappeared!
It was a led spot that was the offender.
So even though I had not set out to mitigate a line noise issue, after accidental discovery, I had it solved in 5 minutes.
A bright spot in a cold gray day.