The release of a vertebrae during a specific chiropractic adjustment is the release of nitrogenous gases between the joint somewhat like the release of flatulence from the bowel or a even a burp 🙂 .
This substance can then release into the surrounding tissues, fascia and muscles and can create a reaction to the adjustment.

Once his has cleared the patient feels much improved with increased mobility and reduction of pain or radicular neuropathy.
If this does not occur and the patient is still in pain then another area is still subluxated or pathology such as arthritic changes and spurs are causing aggravation.
This is where an x-ray is useful.

Audible manual adjustments are not always required or chosen as the technique your Chiropractors treatment of choice.
There are several low force techniques that do not require manual manipulation such as Activator method Sacro-occipital technique (blocking) and Neural Organisation Technique.

The clicking noise is completely normal with a manual type of adjustment and these adjustments have been performed now for over 100 years and have helped many people safely.

If you are concerned with the noise, speak to your chiropractor and remember to keep open communication with all your health care professionals and feel comfortable asking them questions too.