My problem was mechanical feedback causing my turntable to oscillate from the addition of subs sitting on a wood suspended floor also shared by my rack. I first tried dealing with the turntable by upgrading the feet to Raven Black Night that have a built-in spring system. This rig is also sitting on top of a Silent Running Audio platform. While there was a slight decrease in the oscillation, I could still reproduce it at higher volume levels.
I wound up adding Townshend Seismic Isolation Bars to the bottoms of my subs and that completely cured the oscillation. I've decided to now try their isolation pods under the rest of my gear starting with my mono blocks. The Townshend products use a spring system as well, but whatever they're doing they seem to do it well.
Kenny