If you look at the layout here:
https://taweber.powweb.com/store/8cm100_layout.jpgyou'll see that there are two star-grounds (suggested). Also, the 3 big cap cans that are on the right need to be mounted on the side of the chassi. All of them need to go to the power star-ground. Therefore, I used a piece of 14 gauge copper wire to create a bus between the 3 and then link the bus to ground (simplifying the wiring in the process).
However, it turns out that this was causing the hum. To remove it (or maybe 95% of it), each of the cap cans needed to be grounded separately to the star ground point. Each had to have its own separate tab. Kinda weird but you don't ask in this case, you celebrate!