Can't explain why it suddenly appeared in your system, but I had similar issue with VPI tables - Aries 3, Avenger. For me, it was an isolation & feedback problem for sure. The table's mass doesn't help here. I also found it a LOT worse with 3D arms (even Fatboys) than the older metal unipivots, which I actually liked quite a bit. Classics came with metal arms (quite a good one on the Classic 3), but just in case you upgraded to a 3D arm - that will be a contributing factor. Cartridge didn't matter much (I cycled through many MC's).
HW40 feet (or anything equally squishy) are somewhat effective. A Townshend platform or pods will be much more effective.
It was very frustrating. It affects higher playback volumes and it can hit a runaway point.

