[prepress]

I realized that, since having made the most recent changes in the setup I'd been paying attention to the right channel only. This evening, I re-positioned the TT power cord again slightly, and connected the tonearm cable to the MC input. The hum is in both channels, but I turned the volume dial up to 43 before any hum was clearly audible. With no connection you get the standard noise you might expect, too low to be bothersome unless you put your ear next to the speaker. I repeated this with the MM input, and got up to about 48 before hum was audible, again from both channels and almost too low to be audible unless the ear is right up to the speaker; I'd not likely hear it at my listening position (about 9.5 ft. away) at normal listening volumes. In both scenarios, with no music playing and me positioned between the speakers, the hum was barely audible.

Still connected to the MM, I put a record on and could not hear noise or hum at a volume of 44; the music drowns it out if it's still there. By contrast, before I re-positioned the power supply the hum was loud enough to compete with the music (and in the right channel only). I may just reroute the tonearm cable, which does run near a power cord or two, or the power supply's power cord, which is longer and surrounded by other power cords, and call it a day. For all I know this was a problem that existed before, but wasn't noticed because it wasn't loud enough.

Problem not solved, but mitigated significantly when considering where it started.