Super Noisy Phono Pre--Help?

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.

Sounds like Lewm and Jmmorford both have the same problem, and in both cases no evidence whatsoever that the preamp is at fault.

If getting a lot of motor noise the culprit likely has something to do with the tone arm wiring. Perhaps a bad ground so the arm tube isn't able to shield the cartridge from the noise of the motor. If one is using a belt drive turntable, the best designs will have the motor opposite of the arm in order to minimize noise pickup from the motor. But if the motor isn't grounded properly and if its not opposite the arm, the noise from the motor might be getting into the preamp through the cartridge itself.

If the preamp is silent when the turntable is disconnected but on, this is a good indication that the preamp is not at fault.

This would also explain the sudden nature of the onset and why its not tubes (if it was tubes, the problem likely would not have manifested in both channels at once...). All it would take is one bad connection in the turntable and you've got your noise problem.

Dear Ralph, I neglected to mention that the phenomenon I encountered was not present when either of two other entirely different preamplifiers were substituted for the Janus. Further, the noise was present when the tonearm/cartridge was not in use; all one had to do was turn on the tt motor to produce the noise, in both channels. Waving the arm wand back and forth across the surface of the platter also had no effect, good or bad. And finally, as noted, the problem was cured by reducing the lengths of the leads on the coupling capacitors (or cannot rule out that there was a weird defect in one or more of the coupling capacitors themselves, since I replaced the couplers when I arranged for shorter lead lengths). The situation you describe, would, I expect, result in hum or other mixed frequency noise. What I heard was the actual sound of a motor running.