The back crack had a lot of pain. My lower back has minor stiffness today, but it's nothing like the last time I injured it. If I sneeze, it hurts a bit. For the past 3 days or so, I've been sitting like Esther Gokhale suggested, by elongating my spine, and for the first couple days, my back cracked a lot and got stiff. I think now my back has gotten used to it. I wonder if that had any role in it though.
Also, for some reason, when I went with the mixed grip, I just didn't feel comfortable. I'm wondering whether the mixed grip changes the dynamic of the deadlift. I'm thinking of going with the hook grip instead.