Why does my jaw keep cracking?

TMJ. This could be an issue with the temporomandibular joint (tmj). If you just hear a sound while chewing... That is the movement of the condyle of the jaw bone in the joint space. A popping sensation could be a problem with the joint cavity. A pain when chewing or talking could be inflammation of the joint space.
Possible dislocation. A joint that click or cracks may be dislocated or have some other problem within the joint. If you can open and it clicks and then bite on your front teeth and open without clicking, you can recapture this dislocation. Whatever, you will need to check with your dentist for help or a referral to someone that can help you get this under management.