In the same way “popping” your knuckles makes a sound. The majority of the joints in your body have the ability to “popped”, more than you probably think. This happens when negative pressure is created within a synovial joint(most joints of the body). This is a very normal part of a typical adjustment and causes minimal discomfort, if any.
This should not be confused with a “snapping” or “clicking” sound that may be heard when you have injured a tendon or ligament. Those sounds typically occur from friction forces caused by rubbing into other anatomy in the body such as your bones.
You may also experience a noisy knee, elbow, or back as you age. This is actually called crepitus. Crepitus describes any grinding, cracking, crunching, or popping that you experience when moving a joint. Crepitus in isolation is usually no major concern, however if it is accompanied by pain or is preventing you from doing what you like to do then you should visit your chiropractor for further evaluation.