What is that noise during an adjustment?  The sound is just an audible release of gases that are compressed between a bone joint, much like the sound you hear when you crack your knuckle.  The sound is not caused by bones rubbing together or “cracking.”  An adjustment only moves the joint by a few millimetres.  Sometimes this noise will appear louder the closer to your ear it is.  For example, a neck adjustment will appear much louder than a lower back adjustment simply because of the proximity to your ear.