Since this thread is getting over and finished - the woofer pumping has stopped - I will only update if I find some clue, what the problem was. So far, I have not been able to recreate it. Maybe it was caused by a troubled spindle - not quite in place - or other drive problems, as suggested by vpi and others, above. Obviously, the slight leeway between the spindle housing and the plinth, which I need to tighten, may play a role, but in practice I don't think so, since due to the 10 kg platter weight, it settles quite solid anyway, and I cannot reproduce pumping by pushing the platter (or plinth).
I note an interesting thing, checking the player, and cleaning the belts, pulleys and platter. The Hanss uses two very silent motors, not vibrating much. But when I touch the top pulleys, slightly with fingertips, the vibrations are more notable. Sometimes it seems as if the motors develop a "trouble" position with the pulleys straining and vibrating. I can reduce the vibrations just by moving them a tiny bit. This is a behavior I recognize from my VPI HW-19. The motor / pulley does not quite "stall", but a combination of energies has made it stressed. Anyone who recognizes this pattern?
I note an interesting thing, checking the player, and cleaning the belts, pulleys and platter. The Hanss uses two very silent motors, not vibrating much. But when I touch the top pulleys, slightly with fingertips, the vibrations are more notable. Sometimes it seems as if the motors develop a "trouble" position with the pulleys straining and vibrating. I can reduce the vibrations just by moving them a tiny bit. This is a behavior I recognize from my VPI HW-19. The motor / pulley does not quite "stall", but a combination of energies has made it stressed. Anyone who recognizes this pattern?