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

It's a hum or low buzz coming through the speakers...sounds like a ground loop to me. It only happens when I put the stylus on the record (and only when it's moving at 45 rpm). I suppose I could connect the pre-amp outputs to my oscilloscope to prove that it's 60 Hz, but that's what it sounds like to me.

I have to admit, thats an odd problem. Honestly, I'm guessing on this, but you may try 3 things. I assume you have a vpi turntable. On my scout, the motor is completely separate. 1. I would check for a resonance either from the motor touching the table and/or, if not touching, just make sure the motor is sitting securely and everything looks ok. 2. Run an extension cord from another outlet in the house that you know is not on the same circuit as you equipment and start plugging things into it. 3. Watch the record spin at 45, unhook the motor and belt and spin it by hand as best you can. You have probably tried some of this already. I can't think of anything else other than swapping different components out or calling vpi. I wish I could be more helpful.

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?