The popping or cracking sound is simply air that is naturally found in your joints. That air is vacuumed inside the joint and, when pressure is applied, you may hear air release from the joint. It is not related to knowing if you had a “good adjustment.” Some people don’t have obvious air releases but still receive effective adjustments.
For some people, the sound is uncomfortable. We are happy to use other techniques, such as instrument adjusting, that can make you more comfortable.