Back in the early 80's I owned a Technics direct drive turntable with an Audio Technica cartridge using a Kenwood 30 amp receiver. Sound was good but when the music was soft or during start up I could hear a hum.
I've been living with an SL1210 for nearly 8 months now, and it's playing through a much higher resolution system than I had in the '70s or '80s (or a Kenwood receiver, for that matter). And I listen to it more critically than I listened 25 yrs ago.
Mine does not hum, growl, scratch, rumble, or squeal. This past week I lubed the bearing with the officially correct oil and added KAB's fluid damper. Now this thing is spooky quiet. Even when listening through Sennheiser HD580 headphones, I hear no turntable noise. None. Sometimes I hear LP surface noise, but even that has dropped significantly since adding the damper trough.
Hum might have been a cartridge mismatch or a grounding issue.