I was using the S-meter instrument to see what happened as I unplugged things around the house. I guess it is a good thing that the noise dropped from S6 to S4.5, but it means more work for me, hunting down RFI.
The S-meter is a fairly coarse reading. I bet a reading from the audio voltmeter would be much more precise. The dBV reading is relative to the AFV, for some reason.
To get an accurate reading for RF, the instrument would need to always set the preamp and attenuator the same way (probably on and off, respectively) and also turn off AGC.
Anyway, thanks for the S-meter instrument.