Al, I had/have an issue with my Aesthetix Janus full function preamplifier that may be very like the one described by the OP. When the tt is "on", I heard a sound on the speakers that was very like that of a motor, the turntable motor. The sound was only present when the tt motor was running and immediately ceased when I shut it off, and only when the Janus was set to "phono". Extensive investigation suggested that the tt and the Janus were very well isolated acoustically from one another, so I tend to rule out the idea that a microphonic tube was picking up actual motor vibrations. Further, the tubes were not demonstrably microphonic in the first place. Switching outlets and grounding vs ungrounding the tt also had no positive effect. Finally, I faced the possibility that the coupling capacitors in the Janus, which I had force-fit onto the PCBs using longish leads, might be picking up motor noise "through the air". I then replaced those caps with smaller ones that allowed the use of much shorter leads, and this cured the problem. But it was very odd; I would not have thought that EM radiations from the motor could manifest as "the sound of a motor". I wonder whether something similar is going on here.