Lots of turntable manufacturers perhaps did not do the best job at shielding stray magnetic fields from their choice of motors. I also used to blame cartridge manufacturers for this problem, but then I hear of tables that hum with many different makes and models of carts. This is a tough problem to solve, if it can be, short of moving the motor, the motor's power supply or whatever. DC motors with remote power supplies seem to be a great answer. AR used to use a great motor made by,,,,,,by,,,,,,Hayden. It was a 16 pole synchronous motor, shielded. Quiet as a mouse.
Wayner