Willy Mackay is right, however it can also be tendons flipping which makes the sound, which happens to me in my hips. I have always 'clicked' and sometimes it felt like I had to click certain joints as they felt uncomfortable until they clicked. But have since found out that I actually have a dodgy hip, even though I'm 22 and am in pretty good health. If its concentrated in one area, it might be worth seeing someone, as you don't know if there may be an underlying problem - not wanting to scare you, but if there is something there, you can sort it out now while you're young. For instance, my dodgy hip is a sacro iliac problem,that probably started as I was born breach and got worse as I started dancing when I was 13, but I'm now being treated by a chiropracter and should be sorted out soon. Maybe start with your doc and go from there. Hope this helps!