I think most have missed the point, his sub doesn't move, it rattles. The sub only moves if he pushes down on it. I own an SVS sub and have never experienced this, the cylinder shape is so rigid over braced cubes, that it can't rattle. Since this sub fires down at its own wood platform, (its feet are attatched to this platform so the driver does not fire directly at the floor), see if the platform is securely attatched to the sub. If the platform is loose, this might cause the rattle. Are the feet tightly attatched to the platform? Is your floor braced in this area? Put a throw rug under the sub and see if the rattle stops. Are your floor boards level under the sub? Let us know how you make out.