TLDR: The Italian way of doing acoustic, non-destructive testing of a material. This is also done in many other things such as pipelines, chairlifts, and welded

TLDR: The Italian way of doing acoustic, non-destructive testing of a material. This is also done in many other things such as pipelines, chairlifts, and welded metals or machines that have pre-recorded acoustic signatures or sound recordings. Hit it with a hammer, listen to the tone. If it sounds very different, inspect or reject.