Maybe Ralph, the owner of Atma-Sphere, will see this thread and respond.Indeed I did.
I'm pretty sure all that is happening here is that the Supratek has no internal connection on its XLR (since its a single-ended preamp) between pin 1 and pin 3. As a result, pin 3 is picking up noise and the amps are amplifying it.
A jumper installed between pin 1 and 3 on the XLR inside the preamp should sort it out.