Turntable feedback rumble problems with new sub

Upon further review, even with the sub turned off, the the LS50s start to rumble if needle is on record and volume is turned up.  I never really noticed this occurring, probably because I wasn't looking for it.  I've heard that old Technics 1200s have a "rumble" issue, so I'm wondering if its present regardless of isolation efforts.  I ordered some Herbie's Fat Dots to put under the speakers, although I might try them under the Isonoe footers to see if that helps.  @chakster I adjusted the footers as you suggested, which didn't eliminate the problem.  
@millercarbon I don't think I have the skill or tool set to build a sandbox, but amazing pics.
Any thoughts on utility of turntable change, or keep tweaking the isolation.  I haven't seen stuff on springs but I'll take a look.  

Townshend Audio Seismic Pods under the table, the speakers, and the sub.

It’s your TT support brother. You need to decouple your TT from all other negative forces.

Remove the speakers from the turntable cabinet and use speaker stands. Or... remove turntable from cabinet and use turntable shelf.

other end solution, at least partially is a phono stage with a subsonic filter - like on the better lehmann phono stages