why do our bones click?
The funny thing about bones clicking is that it’s not the actual bone that clicks! The clicking noise comes from the joints where the bones meet. You’ll hear this noise sometimes when they move.
The fluid in our joints makes sure the bones move against each other smoothly. Over time small gas bubbles form in the fluid. When the bones at the joint are moved the pressure pops them. This makes the clicking sound. Some people pull their finger joints to make them click as a nervous habit. Most people notice that their joints click from time to time. This could be in every day activities and in general is nothing to worry about.
Sometimes minor damage to the joint, such as a sprain may cause the joint to start clicking. This is because it is inflamed. Once this has healed the clicking should stop. If you have pain, swelling or redness with clicking, or you have any difficulty with movement then the next step is to see a GP.
It’s a good idea to look after our joints – they have to last us a lifetime! This is why we should take regular exercise and make sure we don’t get overweight.
I know it has something to do with compressed gasses in your joints which then collapse rapidly and give an audible sound...but, the wikipedia article explains it better.
It's not certain, as it gives a few theories but suggests the most likely cause.
"When a manipulation is performed, the applied force separates the articular surfaces of a fully encapsulated synovial joint, which in turn creates a reduction in pressure within the joint cavity. In this low-pressure environment, some of the gases that are dissolved in the synovial fluid (which are naturally found in all bodily fluids) leave the solution, making a bubble, or cavity, which rapidly collapses upon itself, resulting in a "clicking" sound."
From here: http://funadvice.com/r/bhdbq77vm77