I am not sure what i do to my back but ...

I simply lie on my tummy with my arms down by my sides and then force my pelvis down onto the mattress (find that lying on the mattress is the only thing that works using this technique!)
OR
I lie on my back on a hard floor with my arms to my side and I feel a slight discomfort or displacement in my lower back... at this point I breath deeply in and out a few times and usually it pops (is the best way of describing it!) And I feel like I am lying perfectly flat on the floor

What is it that pops????