THe least expensive with the no mods allowed to room is mass under.. Patio slab. bricks... Anything that weighs down the floor so it no longer bounces it the 'just right' frequency (it is now at). a pile of cement bricks, a large patio slab or four... on the floor under around on the rack bottom. I promise it will change the issue. A two foot round two inch thick slab weighs around 80 pounds... Or square ones.. or small bricks...