The good news is that (other than the pain) it is completely harmless.
The way it always felt to me is like someone wrapped a small wire around something tender in my chest, and if I tried to breathe or straighten my posture, they would yank on it. I’d get it anywhere from a couple times a week to once a month. Then one day in my mid-30s it just stopped.
From what I understand this is relatively common. I was so grateful for the person on reddit who dropped this nugget of wisdom several years ago. It was nice to know I wasn’t dying or whatever.
I can also sometimes get it to snap by putting my left foream against a doorframe and twisting my torso rightward to stretch my chest. I’ve always thought it was “popping my sternum” but it only works/is necessary on the left side