There are basically three things that will cause your joints to make a noise.
The most common in my estimation is gas trapped in your joints being quickly released forming bubbles in the process which make the popping sound. Some background, your joints are lubricated by a substance called synovial fluid. This compound contains gases, primarily nitrogen and carbon dioxide. They are contained in the joint capsule. The quick stretching of this capsule causes the quick release of the bubbles. This is what you hear during a chiropractic adjustment.
A tendon is structure that holds a muscle to the bone. A sound is sometimes created when the tendon snaps on a quick movement or slides over an abnormal bump in the bone that the tendon passes over. The popping sound you hear from your ankle when you move it quickly after it has been immobile for a while, say when you’re watching TV, is a tendon snapping.
Finally an arthritic joint surface will make a sound. This isn’t the popping sounds as mentioned above. This is more of a grinding sound commonly heard when you have neck arthritis. It’s easy to hear it in your neck because it’s close to your ears.
This sound is created by the joint surfaces which are normally very smooth. The joint surface is covered by hyaline cartilage. As you age this cartilage begins to fall off or pit. The pitted surfaces then rub together instead of gliding on each other creating the grinding sound.
If you get nothing else from this blog series remember this. Never force a joint to make it pop. Even though people who do finance my vacations, it is wise to avoid this activity.
Cracking Knuckles Part 1: here
Cracking Knuckles Part 2: here