Is there a sound-deadening mat for the iMac?

I'm rearranging my desk at home and also shifting the equipment around a bit. What I've found is that the iMacs - though relatively quiet, but not miracle workers - are transmitting a small amount of vibration to the desk which is contributing to the overall noise level.

I'm wondering if there's a specific answer for that issue. If not I'll probably hunt for some very dense sheets of thin rubber and then run it thru the cutter to shape it, but if I don't have to do it myself, all the better.