The hum is probably not coming from the electronics of the table. You might have a broken ground inside the arm. Rega solders the ground wire to the inside of the arm tube.
Make sure all the headshell (armtube) wires are tight onto the pins of the cartridge. Even though the cart was preinstalled, you never know. Double check the left channel wire/pins since the hum went away once you disconnected it.
Make sure all the headshell (armtube) wires are tight onto the pins of the cartridge. Even though the cart was preinstalled, you never know. Double check the left channel wire/pins since the hum went away once you disconnected it.