Parts of the house foundation sound hollow...?

Question

When I tap the walls in the foundation (basement) some parts sound solid and others sound hollow. It mostly near the bottom that it sounds hollow. Could this mean that the foundation is damaged?

Answer 1

You are probably hearing the difference between areas that have re-bar (steel) underneath, and places that do not.

Answer 2

If it is a block wall, you could also be hearing the void spaces in the blocks.