I have used weight on top of my CD transport with metal cones on the bottom to good effect. The additional weight really couples the unit to the rack which in turn is anchored to the floor. If you are using isolation type such as rubber feet or damping material on the bottom, I am not sure the additional weight does anything. I went to a golf shop and picked up 5lb lead ingots for cheap to use as weight. They get these for use in customizing clubs.