physics shaking

I use Sumo for the realtime engine. I set a box on a plane and made the box actor/dynamic/rigid body/bounds box. It works cool when i hit it, reacting realistically. However when it sits there without me hittingg it, it shakes a bit, nothing crazy just like a bit. i noticed other demos i tried it does the same thing. I put 2 boxes 1 on top of the other and assigned the rigid body to it and it shakes all over the bottom box. Anyone know how to fix this?

Increase damp I think.