A hollow-sounding floor can be a surprise, but it is normal and not considered a product defect.

You may hear hollow sounds where your subfloor’s surface dips or has ridges. This does not affect the integrity of the installation of the flooring.

Also, when it’s cold, tile tends to be colder than other flooring surfaces. Since tile is hard, it can be noisy, or  produce a hollow sound, when walked on.