The rack is vibrating the floor and causing the entire building to vibrate. I need to mount it on something to absorb the vibration. What material can I use, and where can I obtain it? The weight of the rack will be approximately 150Kg, so not particularly heavy. It is on four castors, which are themselves resting on 8x2 planks, which are resting on the ceiling joists. The most sensible place to put material is probably between the planks and the joists.