The body of the bass that I'm making is quartersawn bubinga, and today I started my finishing sanding. I get to the "butt" end between the straplock and the jack and I see what appear to be scratches in the end grain running horizontal to the top (actually, they're at a bit of an angle...about 20 degrees to the horizontal axis: if the bass were laying down and you were looking at the end, they run from slightly lower left to upper right). Anyway, I'm sanding and sanding, and they won't go away. Turns out that they are hairline cracks. Is this called "checking?" What can I do to make sure it's stable? There's no seperation in the wood, but I want to be certain that it's can/will be taken care of. I've attached a pic: hopefully you can see what I'm seeing.