Yes its possible no matter what the table is on the Planar 3 itself can still vibrate if you get the energy in the air high enough. Especially if you're using it with a dust cover. If you are that would be the first thing to go.
Granite is great for mass and dynamics. My amp and turntable stands both use granite. But granite also rings. Badly. My turntable rack greatly reduces this with a sand bed under the granite and BDR Source Shelf between the granite and the turntable.
Try putting the granite direcly on the table top. Try something like sorbothane or blu-tack between the granite and the table. Anything, absolutely anything, will be better than what you have now. The points aren't isolating, they're actually maximizing vibrations by allowing the granite to ring.
Also highly recommend a small sand bed between the turntable and the granite. Won't eliminate feedback coming directly through the turntable but it will be a big improvement over what you have going on now.
Granite is great for mass and dynamics. My amp and turntable stands both use granite. But granite also rings. Badly. My turntable rack greatly reduces this with a sand bed under the granite and BDR Source Shelf between the granite and the turntable.
Try putting the granite direcly on the table top. Try something like sorbothane or blu-tack between the granite and the table. Anything, absolutely anything, will be better than what you have now. The points aren't isolating, they're actually maximizing vibrations by allowing the granite to ring.
Also highly recommend a small sand bed between the turntable and the granite. Won't eliminate feedback coming directly through the turntable but it will be a big improvement over what you have going on now.