Any thoughts on a solid hickory platform under my tt

Adding to Geoff's comments the vibrations he describes (earthquakes, construction, passing cars) are very real and the effect of removing them (in my case by isolating my speakers) is profound. This is quite different from the normal (and also relevant) concern of isolating your components and sources from the effects of the speakers in the room

The following link from Townshend is a nice explanation with data

http://townshendaudio.com/PDF/Earthquakes%20on%20Hi%20Fi.pdf