The first step you should do, is to look for a rack with an adjustable Top Plate to level the Turntable (This is really important). Solid Steel - from Italy - has made such racks, maybe they still do it, when not, they probably have a cost controller now.
Next is a useful isolation System, go for a serious one, not for a polished piece of wood for 2k or similar plastic toys, go for a stand which is used for electron microscopes (serious development, not high end standard). Vibraplane or Minus-K are the right ones. They also isolate the table from outside influences. I use 3 of them and never looked back.