What causes my back to click?

Back clicks are typically caused by the release of gas bubbles from the synovial fluid, which acts as a lubricant for the joints. When your spine moves, the pressure changes can cause microscopic bubbles to form in the fluid and when these burst that makes the clicking sound.

Sometimes you might even "crack" you own back intentionally which also cause gas-bubble cavitation. Another factor can be the rapid movement or sliding the facet joints that are found between certain vertebrae when they have moved out of a neutral position. They can catch slightly which then suddenly give way, releasing built-up pressure. As with gas bubble popping this often can feel quite satisfactory which may explain one of possible reasons we like cracking our knuckles or toes for example. Lastly there can be snapping ligaments or tendonds and sometimes the rib moving as we breath can get "stuck" which can pop out when moving around which may result in a back click.