I noticed when playing some loud bass demos I got a clacking noise coming from my sub. I assumed this was the sub bottoming out at first. But then I noticed it seemed to come from the box not the driver. Then I thought my box was falling apart. Finally I discovered my box is moving while it plays and the clacking goes away when I sit on the box to keep in on the ground. I'm surprised this can even happen when my SBB4 Tempest weighs nearly 190lbs. Is this normal? Is it due mostly to the downfiring position of the driver? What do you think I could do to prevent this? Would bluetac on the bottom of the subs legs be enough to stop it?