Turntable resonance normal?

Hi folks. I've noticed that with my Soundsmith cartridge in the groove without the table spinning if I tap on the tonearm, plinth, or HRS base I hear a thump with volume set at normal listening level thru the speakers. Not real loud but there. I don't know if this should happen given my setup. VPI Prime Signature with the Fatboy arm sits on an HRS base which sits on an Adona rack. No noise when stylus is out of groove. Am I expecting too much or am I missing something? Any input is helpful, thanks. Joe