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

I'm having a problem with a ground loop that appears to be associated with the VPI SDS/motor that is present only when running at 45 rpm (not 33 1/3). Has anyone else experienced this? Did you solve it?
I have a VPI and SDS. Can you tell me a little bit more about exactly what you are hearing?
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,
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.
I already tried the VPI motor oil. You just put a drop on the top of the spindle, right? I don't see where you tighten the black plastic pulley.
On the side of the pulley below where the belt attaches, on the side of the shaft you should see two small openings 180 degrees from each other. A small Allen wrench fits into both. Make re they are snug. It's how the plastic pulley is removed from the motor and gets loose over time.
Is it on the black piece where the belt attaches? I don't see any small openings. There are two groves, either for the belt to fit in, and a flange just below them. The whole piece clamps down somehow on the motor's axle, but I don't wee any allen screws holding it on.
I also did some testing with my SDS. I changed the voltage from 102 to 96 and 108, and both of these voltages actually made the noise much worse.
If you have a stand-alone motor the are on the plastic flange that covers the motor's metal axle below the pulley.

Plug your motor into the wall outlet and remove he SDS from the system. If you have a pulley that has two different places to put the belt on (33 and 45). Try them both. If no noise, this probably isolates it to the SDS.

Unplug the SDS. Then plug it back in again and try the motor controlled by the SDS again. See if noise comes back.

If you have tried all these things including proper motor lubrication, then it may be time to call VPI and talk with Mike. If you have to call, make sure you have written a list of everything you have tried so it will help him quickly eliminate etiologies and treatments.

Good luck. It sucks when something goes haywire.
The pulley has two different places, but they're the same size, so can't be 33 and 45. It only runs at 33 by itself as far as I can tell. So, can't tell if it's the motor or the SDS. It could be the motor, the SDS, or their interaction.
If you have a single size pulley, it's meant to be used with an SDS. If you talk with VPI, let us know what come up with and how it turns out.