grado reference statement hum

Grado's are notorious for the poor shielding of the cartridge, which in your case is picking up hum from the TT's motor. Used to be a problem for me until I got a TT with a well shielded motor. I've seen suggestions in the past for shielding motors. Perhaps some one will chime in with some suggestions.

hopefully someone will know how to shield the motor. I like the sound but hate the hum. The ply was way too "digital" for my tastes

try the mu metal shielding material

where does one obtain mu metal?

Is the motor on your Wilson turntable directly underneath the platter? What I have seen some do in the past is to place a thin sheet of aluminum foil underneath the turntable mat. This will create a shield in-between the cartridge and the EMF fields being created by the motor.

This is ineffective if the motor of off to the side. But if it is directly underneath, it may be an inexpensive way to create some shielding without breaking the bank.