The last time I researched why joints pop and crack, the consensus seemed to be "no one really knows!" I think I remember hearing something about calcium deposits, but from what I've read any explanation at this point is hypothetical (isn't everything?) - I do notice that some days are much, much worse than others, with people just staring at me because every movement is so loud with all the cracking! Interesting topic to research, though - sorry I can't be much help!
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