We recently had to buy a new microwave. It was doing fine except for an annoying rattle in the case. I pressed here and there, and finally found a place where I could stop the noise. I put my scale on the spot to see how much pressure was needed, and it turned out to be just a little over five pounds.
The stainless steel ball I salvaged from a three-inch valve several years ago weighs six pounds, and it stops the rattle very nicely.