turntable issue - faint hum on one channel

Just got a phono board installed in my Arcam AV8. Picked it up yesterday, and have been playing vinyl all day today. Sounds great, even better than the Rotel RQ-970BX that I just removed from my cabinet.

I was removing the Rotel unit from the cabinet, and started adjusting the rat’s nest of cables and wires. As an experiment, I set the input on the AV8 to turntable, turned the volume way up on, and listened as I moved cables. Sure enough, a bit of low level hum came and went. It seemed to track the turntable power cord at first, but then I learned a hum was present even if that cord was completely disconnected. After an hour of work, I tracked the hum to the wire leads on the turntable wires which connect to the phono cartridge. My turntable is an 15 year old Thorens TD-280, with a newer Shure V15VxMR cartridge. The wire connectors had some corrosion. I pulled the leads, and then used some naval jelly and some 400 grit sandpaper to rough up the leads. The pins on the cartidge looked fine, so I did nothing to those. I re-connected everything, and turned the volume way up again.

The hum is reduced susbtantially, but still present. It is higher on the right channel. Left channel is almost dead silent at high volume. Right channel hums, and when I touch the red wire on the cartridge the hum gets louder. This is only present at high volume though. It is just barely audible at normal listening volume when I am a few feet away. Still, I’d like to eliminate it, you know?

Any insights on eliminating this hum completely?