The “popping” or cavitation noise heard during a chiropractic adjustment or manipulation is a release of a carbon dioxide gas vacuum from the joint. It is much like the popping noise heard when you open a bottle of champagne! In the overwhelming majority of cases this is not painful when applied by a properly trained practitioner. If you do not hear a popping or clicking sound this does not mean that the adjustment or manipulation was ineffective. There are many chiropractic adjustments or manipulations that produce no sound at all. The intent of the adjustment or manipulation is not to produce a sound but to improve function in spinal joints and stimulate the nervous system.