I remembered your post and think I may have a solution for you if you are still struggling with this. I know this is late in the game but better late than never.

I just recently cured a very similar, if not the same exact problem. Assuming what you were hearing was a 60 cycle hum (60 Hz), here's what I would recommend and what I did to get rid of that annoying hum. Make certain all the connections to all your components are wired correctly and secure (i.e. no lose or dangling connections). Make sure the AC connection and the connections to your surge protector are secure, as well. Then, make sure your power cables aren't right on top of one another or on top of your surge protector. Put as much space between them, as possible. Do the same with all your other cabling & wiring (i.e. interconnects; speaker cables; etc.), as well. The idea is to put as much space or breathing room between all your cables & wires as possible. If that doesn't do the trick, put as much space between your turntable and amp as possible. The idea here is to put as much space between the cartridge and the location of the power supply in your amp as possible. Depending upon your components, you might be able to achieve this by just swapping the positions of the amp and turntable. If this doesn't do the trick then I'd have to ask if, perchance, you might have other components on your rack that might be causing the feedback. For example, a satellite TV receiver or two? I recently terminated my DirecTV service and got rid of 2 satellite receivers (one for regular TV and one for 4K ultra high definition TV) that were located on the shelf of my rack just below the amp. I can't be absolutely certain of this but I suspect those satellite receivers had everything to do with my turntable hum problem.

Good Luck! Just out of curiosity, please let me know how you make out with all of this. Always curious.