Ground loop related to VPI SDS/motor at 45 rpm?

If it only happens with 45rpm and not 33rpm setting, it sound like something is wrong with the SDS

That sounds as if it could be motor noise. If it only does it when the stylus is in the groove, I doubt it's a ground loop. At 45rpm, the noise is brought up to the hearing threshold. I didn't have the SDS with my Scout, but I did have quite a bit of motor noise that took some measures to eliminate. I wound up modifying the Brightstar Audio platform with a cut-out for the motor, and supporting the motor on the wall mount platform with a riser and isolation between the Target platform and the riser.
I hope you get it licked, these things can drive you crazy.

Best regards,
Dan

I have since moved and am still getting a mid-frequency noise, but now it only seems to be coming from the motor itself, not being transmitted through the speakers. It's pretty loud. I don't have cones on the motor, just the original rubber feet. Do you think cones would help?

2 choices
1-lubricate the motor
2-call VPI

If you haven't oiled your motor in a while, it might be time. Although I never had a hum or noise through my speakers, when I owed an Aries 3 the motor would hum ar 45rpm audibly when I placed my ears around 12 inches away from the motor. I fixed it by tightening the black plastic pully on the motor with an Allen wrench and oiled the motor with a couple of drops of VPI motor oil.