THis joint is at the very base of the spine and is basically where the spine connects to the pelvis - hard to explain, but it is definitely a vertebral crack I am experiencing. THis is largely the most invigorating crack - it has a sound that comes from deep within my body - I cannot imagine how loud it would be were this joint not covered by a bunch of skin and were it not so deeply buried inside the middle of my body.
I am surprised that it doesn't cause pain - I fear it cracking the wrong way sometime and having ot go the chirporacotr, but I'll take my chances!