It may a combination of the Motor RFI/EMI and a tonearm grounding issue
Try testing for continuity across the ground wire and the tonearm - if that is OK then your cartridge is sensitive to noise from the motor. Grado carts used to be very sensitive to noise from the Rega motor.
I have not had an issues since I had the tonearm wires replaced with a Cardas one piece loom.
I now have an Audiomods arm with a one piece loom - it is now very quiet.
Regards - Steve
Try testing for continuity across the ground wire and the tonearm - if that is OK then your cartridge is sensitive to noise from the motor. Grado carts used to be very sensitive to noise from the Rega motor.
I have not had an issues since I had the tonearm wires replaced with a Cardas one piece loom.
I now have an Audiomods arm with a one piece loom - it is now very quiet.
Regards - Steve