Damping Rega Table

Herbie's isolation feet beneath the solid undersurface might help your problem. For more money, Aurios MIB footers under the solid undersurface, away from the built-in factory feet made magic for my turntable, but it is weird when a turntable has "floating on air" feeling while putting on a record, or manually placing the cartridge onto the record surface. Also, the use of the "Non-felt mat" helped give a clarity and solidity to my records compared to the factory record mat. Lastly, with Rega RB-300 arm, using the Titanium Heavyweight counterweight unexpectedly made the single greatest improvement in the sound of my records.

An alternative to sorbothane feet are the ribbed rubber cork centered footers sold by Rcreations on Audiogon at a bargain $10 per set of four. Using three footers avoids wobble of the platform being supported, and you can check with this vendor if your concrete slab weight is within the capabilities of these footers.