As you can see, there can be a whole lot
of reasons
I know exactly what you mean. I get them
from every conceiveable spot...even the
middle of my chest bone

Heck, I am only 29
but I sound worst than my grandparents!
The main reason why some joints "pop" and
"crack", is that most joints has fluid in
between them, that lubricates the joint.
When, for example, you crack your fingers,
it's a release of gas bubbles in the
sinovial fluid that makes the noise.
It might also be attributeable to
hypermobility...
Do you find that your joints are unusually
flexible? Also, do you ever get a lot of
joint ache's and pains, especially when
walking long distances?
P.S. Nice to see a fellow SA here Beline