Grado/Rega hum is well known & documented. I tried a Grado 25 years ago (before the Internet as we know it) and ended up selling the cartridge.
Changing cartridges is the only sure fire way to eliminate the hum.
Almost any other cartridge works with Rega TT’s, but the grado unfortunately is not one of them.
Other cart’s I have successfully tried include Rega, Nagoka, Goldring, Denon, Ortofon and Audio Technica.
The Humbucker listed above may work, but I did try shielding by covering the inside of the motor compartment on my Rega with foil and grounding it and whilst it made a little difference I could still hear the hum once the cartridge reached the run-out grooves at the end of a side
Not much help - sorry