An audible pop is the sound that can derive from an adjustment in spinal manipulative therapy and is often seen as an indicator of a successful treatment. 

This systematic review showed:

This review suggests that the presence or absence of an audible pop may not be important regarding pain outcomes with spinal manipulation.

Moorman, A.C., Newell, D. Impact of audible pops associated with spinal manipulation on perceived pain: a systematic review. Chiropr Man Therap 30, 42 (2022). https://doi.org/10.1186/s12998-022-00454-0