I know this must sound like a broken record (especially on this string) - but I can't believe I found you lot... I've had this for a while now (about 5 years) & having read most of the literature on the web about this strange condition, I'm still none the wiser about how I got it!
Here's the conclusion I've come to: I've been asthmatic since I was 4 (some people say this could be an issue), I've been skateboarding for 15 years (I've landed on concrete from a height more times than I care to remember - this is obviously not 'good' for me), I broke 2 of the upper left hand side ribs in a snowboarding accident about 5 years ago (a chiropractor once told me that I was sub-conciously protecting my damaged area around the ribs and my muscles were in knots because of the way I've been carrying myself since the accident - hence the pain), my posture is shocking and has been all my life. Anyone of these could be good reason for developing this symptom - but I really noticed it getting worse when I got my first computer.
I was never much of a computer geek, more of an outdoor kinda guy, but when I started working on my laptop regularly (10-12 hours a day) I got really sore & tense around the chest & I really could get some respectable deep audiable snaps out of my sternum. I was really worried at first & like most people that have posted on here - I sought medical advice with my doctor, went to an ostoepath, a chiropractor & someone who specializes in the Alexander Technique (which helped the most actually) the only thing I didn't do was have an X-ray, I wanted to have one to make sure everything was OK - but most doctors thought I was being a hypochondriac. God bless the NHS.
So, I really think my posture when working on the computer is the main culprit of this condition as the pain / cracking started almost at the same time I got my first computer and began to change my daily routine around it. Us human's are supposed to be out there doing their 'hunter/gathering' thing, not stuck in a room staring at a computer screen all day - it makes sense to me that this is a postural condition from 21st century living. What do you lot think?
Anyway - my symptoms - I feel the pain on my Sternum build & when I stretch out to relieve the pain it feels as if my muscles / tendons on my ribs are pulling against my sternum then when it finally does crack it's like a deep shockwave going through my ribcage then the sternum feels sort of cold and painful to touch - but then I feel OK - like I've got a full range of movement again... until it builds up again. When it's bad this can happen 4-5 times a day.
Anyway, I've found this never goes away, just comes in waves. I've tried to pay attention to what makes this worse recently and it seems to me that when all is going nuts at work and I'm stressed & don't have any time to exercise - I crack alot more. This could be because all my muscles crunch up and I'm completely unaware of my posture or it could be a psychosomatic condition that is related to my state of mind. This last part makes sense because when I go on holiday or am in a postitive & relaxed state of mind it seems to ease off... is this the same for everybody else?
I'm no doctor, but I reckon if you try and stay in a positive mind state by eating well, exercising when you can & try and find a release for your emtions rather than bottling them up - the cracking will ease off. I'm not saying this works for everyone, but it sort of works for me & even though life gets me down every now and then - if the cracking starts again - i know its time to readjust my attitude a little.
Just to finish - most people have said how addictive the cracking is - I agree completly, it feels so good when it finally goes. But I guess it can't be good for you & I'm trying to stop 'intentionally' cracking - but it's hard to break a 4 year habit!
Next time I feel a crack coming on, I might film it and stick it on Youtube to see how may off us out there has this...
Later.