So it's interesting to work backward on this.
Grounding wire issue? If so, then the hum should be there no matter where on the disc the tonearm is.
The grooves towards the spindle tend to be less bass-heavy and more out of alignment then the two null points before them (that's why, for example, Peter Gabriel's "In Your Eyes" was placed at the start of the B side of the LP; because of its heavy bass line), so is your cartridge picking up noise? But...
The hum's there no matter the cartridge, so it sounds almost like an internal issue - the tonearm wires; the AC motor.
Let us know what Rega says.
Grounding wire issue? If so, then the hum should be there no matter where on the disc the tonearm is.
The grooves towards the spindle tend to be less bass-heavy and more out of alignment then the two null points before them (that's why, for example, Peter Gabriel's "In Your Eyes" was placed at the start of the B side of the LP; because of its heavy bass line), so is your cartridge picking up noise? But...
The hum's there no matter the cartridge, so it sounds almost like an internal issue - the tonearm wires; the AC motor.
Let us know what Rega says.