Thanks for all the feedback.
My audio rack is in a dedicated space in the living room, so without major upheaval, my outlet options are limited.
First I tried plugging into the only single outlet/breaker combo I have, (one I added in the garage for workbench power) it required a long heavy-duty extension cord and didn't help. In fact it was louder with the TT motor on, the opposite of the situation with the TT plugged directly into the shared "high grade" audio outlet.
Second I tried plugging into an outlet closer by, but on another circuit, requiring a much shorter extension, still no luck.
So...off with the motor cover and back into the system. With one end of a wire connected to the Reduction ground post and the other touching the motor body.....progress.
With the volume set higher than I normally listen the noise was greatly reduced, and once the TT was switched on it dropped into the very low system noise. You have to really listen for it mixed with the ambient noise that slips in through the closed back headphones.
For now I will make the ground "permanent" and see if I can live with the fix.