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

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.