Wildly fluttering woofer

So the problem was not feedback.

A noisy tube in the phono section is still at the top of the list.

Still could be feedback. The replacement preamp may have a built in subsonic (rumble) filter or simply not have the low end response that the Audible Illusions had. Herbie's audio lab sells isolation devices, that curing the problem implies feedback was the issue.
BTW-The original post failed to mention a key issue-"recently moved speakers and placed components on a new rack". That says it all. Much different than "without any kind of warning".
Rolling tubes in the preamp may alleviate the problem as well, if the new tubes have a "thinner" sound. A "military" tube might be a better solution, they're less microphonic by nature because they're built tougher with extra support rods and mica's. The bottles may also be shorter and more compact, less likely to sympathize at the offending frequency.

Regardless, it was a learning experience.

Dear Heyraz, After all the repositioning everything was fine for the two weeks after I installed Herbies devices. I'm waiting to hear how the preamp checks out. Thank you for taking the time. Katz1

While you're waiting for your preamp to come back, you might find some of these tools at the Vinyl Engine website interesting.

http://www.vinylengine.com/cartridge_database_tools.php

Heyraz, the argument against feedback is that when it was happening, it was only in one channel. If it was mechanical feedback it would have been in both channels. The two phono channels of the preamp are right next to each other.