@fsonicsmith
Nothing is wrong with Aluminum; to the contrary, it is a superb material for almost anything mechanical (there is a reason supercars are built from it). It rings because it is very stiff, and that is usually a good thing, but because it is very stiff (and light), it is very easily damped. So if you dampen Aluminum, you get the best of both worlds; stiffness yet well damped composite. Steel or cast iron is a different matter. It is stiff, but weighty and therefore hard to damped, usually not a good material for anything audio (unless you are building a bell).
Nothing is wrong with Aluminum; to the contrary, it is a superb material for almost anything mechanical (there is a reason supercars are built from it). It rings because it is very stiff, and that is usually a good thing, but because it is very stiff (and light), it is very easily damped. So if you dampen Aluminum, you get the best of both worlds; stiffness yet well damped composite. Steel or cast iron is a different matter. It is stiff, but weighty and therefore hard to damped, usually not a good material for anything audio (unless you are building a bell).