Yeah I used to ask my chiropractor the same question: why does my back crack so much? And his answer: you don’t need to worry about the sound, but you should definitely try to strengthen your core muscles to give your back a stronger support. Core muscles, that is, basically back muscles and abs, are very important in maintaining the stability of the spine. If your core muscles are strong, then your spine is better supported and protected and thus less likely to get hurt. I have been doing core strength conditioning for quite a while now and my back just feels indestructible. The cracking sound is still there if I stretch (or overstretch maybe) my back, but that doesn’t bother me anymore. The only thing you should not do is perhaps intentionally crack your back on a regular basis. I think my doctor friend once told me that this would cause your cartilage to wear out more quickly.