Debuzzing a Wheaton TriPlanar problem

Can you tell whether the cartridge body itself is vibrating so as to feed back into the tonearm wand? That is the only mechanism I can think of for this strange phenomenon. If you ignore the problem and play an LP, what happens? Is there added hum coming out of the speakers in addition to directly from the tonearm? Have you tried changing cartridges? If the insulation on the tonearm leads has a defect such that one of them is in bare metal contact with the tonearm wand, I still don't see how that would cause the phenomenon you report. The odds are vanishingly small that there are TWO defects, one on each lead such that there would be a voltage delivered to the tonearm wand (maybe). But strange things do happen.

Sometimes grounding everything to everything is a bad idea. Try removing some of those ground wires. But on the other hand, your report is clearly out of the ordinary; as you know, 99% of the time grounding problems manifest themselves on the amplified audio signal only, not in the form of causing vibration of an inert metal part.

Thanks for your considered response. My former career was as systems software developer, and I appreciate your debugging skills. Occasionally (of course) there is feedback while the stylus is tracking the groove. My gut reaction suspects some sort of intermittent feedback. as you suggested, from the cartridge itself. It is an AudioQuest 7000 now some 15 years old and my new Masseto preamp deserves something better anyway. I'd hate to think it's the shielding on the Cardas cable touching the tube, because that would require a re-wiring but that's what my hands-on experience feels like. Cartridge replacement first, then rewiring. The multiple groundings were done to successfully eliminate a constant hum at table installation time.

Dr_John, I think I did not read your first post all that clearly. Now the problem sounds to me like it might be a sort of RF oscillation in the preamp. I would not characterize this as 'feedback'... it sounds like either a very bad ground or RF in the system. The fact that you can touch the arm tube and have the sound go away for extended times suggests that its an RF problem. I don't think its anything with the Cardas cable, as when you touch the arm tube, you should at that time be able to keep the arm still.

ok - another piece of evidence to add, and this may be the most telling. When I grasp the finger rest at the end of the tube, the hum gets really loud. Just squeezing the tube itself ever so lightly stops the noise. And this part baffles me - all I can think of is a defect in the cartridge.

RFI/EMI problems at tonearm wires can tend to jump around unpredictably as you describe and vary in proximity with the human body. Grounding the tonearm or TT is sometimes not enough, and screened tonearm wire may be necessary to resolve the problem.

Does the hum continue when the cartridge pins are disconnected from the tonearm wires?

You might experiment by relocating the TT to another part of the room. The current location may be in a bad RFI field or too close to in-wall AC wiring or to the AC PS of another component.