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Joe, why would you expect to NOT hear a thump when you tap on the arm or plinth? The cartridge is rigidly attached to the arm (hopefully!), the arm to the plinth (likewise). You hear a thump when you tap the HRS base because the table is a non-suspended design. Tables with a floating sub-chassis (such as VPI's earlier HW-19) provide a degree of isolation between their outer base/frame (and therefore the surface it sits on) and the floating sub-chassis, the feet on non-suspended tables generally don't provide much isolation between the table's plinth and whatever it is sitting on.
What you ARE entitled to expect is to not hear a thump when you tap on the surface the HRS is sitting on. The HRS is supposed to provide isolation between what it sits on and what is sitting on it. If it doesn't, look for a product that does. I recommend and use the Townshend Audio Seismic Pods. VERY effective isolation. The IsoAcoustics GAIA isolator has found favor amongst VPI owners, as they have testified to on the VPI Forum.
Joeyfed, yes this is a problem shared by most fixed plinth turntables except perhaps the real massive ones like the big Kuzma. Sound in the room is transmitted to the base and picked up by the tonearm. You can thump all day long on a suspended SOTA and you will not hear a thing. If you tap lightly on an SME you won't hear anything. Same is true of a Basis and I suspect an Air Force. But, only the SOTA comes in at a reasonable price.
In most cases the noise that gets through is greatly attenuated. I am not sure if it makes a real difference as I have only used suspended turntables for decades.