I assumed it is not such a serious issue.
It is a most serious issue......
We have found that suspended concrete floors have intense inbuilt stresses because of the spans......and these stresses cause lower ever-present Structure-Borne sound than those present in suspended timber floors.
Modern high-rise apartment buildings are particularly susceptible because of the prevalent use of prestressed concrete floor slabs which allow for thinner thicknesses and less steel reinforcement.....but also permit greater movements, bounce and structure-borne sound between 2 Hz-10 Hz.
These frequencies are almost impossible to eliminate from floor-mounted stands and that is why your turntable and phonostage are sounding differently with each and every change in support material.