Try sand bags, or as Elizabeth mentioned rubber. You can go to McMaster-Carr and order a sheet of 40 durometer rubber. Make a nice sized square or rectangle, then place it on the component. On top of the rubber you can place some additional weight like a piece or metal, stone, or wood. Take a look at the HRS isolation devices as they use similar techniques and charge quite a bit for their products. I used their damping plates for a while and liked them a lot, but they are DIYable.
I would attribute the sound you were hearing to be the result of metal to metal contact. Having an interface between the metal might help (you might get the same result with just a piece of granite on top of the component).
I would attribute the sound you were hearing to be the result of metal to metal contact. Having an interface between the metal might help (you might get the same result with just a piece of granite on top of the component).