Avatar, I am glad to see you still posting; what an asset you have become to this site.
Popping your knuckles or clicking your fingers is not as bad as you may think. The usual argument is that it causes arthritis but research shows this not to be the case. Like anything when done to excess, other types of damage may occur with such things as stretching of the surrounding ligaments and a decrease in grip strength.
The sound is produced in the joint when bubbles burst in the Synovial fluid surrounding the joint.
The gas itself is always there but dissolved in the thick clear Synovial fluid. When you pull the joint you decrease the pressure therefore reduce the amount of gas the liquid can hold. This is called cavitation and is the same thing as what causes the bends or bubbles to appear from nowhere when you open a bottle of pop; a decrease in pressure reduces the amount of gas the liquid can hold.
After a pop the gas should take half an hour to re-dissolve again so, until this happens, you will not be able to repeat the noise in that joint no matter how hard you try!