I have that clicking, too!
I was just reading your post from awhile back about something clicking in your neck near your collarbone. OMG - I have that. In fact, I have it all over my body now and they don't know what it is. It's getting worse and causing a lot of pain now (after a year of that clicking/snapping) and I was hoping maybe your doc figured yours out. I can make it snap/click just by tensing my neck muscles in front - like I'm pulling up/flexing my neck with those muscles. It clicks more at times, less at times, and still goes away at times. But, it's doing it more than ever, now and I'm getting scared. It feels like my ligaments are disintegrating in my entire body. The docs have no clue.
I go in for another full body bone scan and mRi's of my entire spine next week. Let me know how you're doing and if you've figured otu what causes that clicking in your neck.