You should have a professional installer check the installation for soundness. It may have not been installed properly. The hollow sounding tiles is an indication that areas under the tile are not in contact with the setting bed. These hollow areas have the potential to cause cracking.
TIP If you intend to grind this floor you may crack several tiles. I would be prepared to replace these tiles or try honing or grinding using a light machine.
Article ID: 559
Created: January 20, 2022
Last Updated: January 20, 2022
Author: Pam Freitag
Online URL: https://sr-manual.com/kb/article/my-customer-has-mentioned-that-when-she-walks-across-her-marble-floor-wearing-heels-whe-can-hear-a-hollow-sound-under-several-tiles-and-wants-to-know-if-this-is-normal-or-should-she-be-concerned-559.html