There's a product used on cars, when repainting and when dealing with rust. I do not know what the product's actual name is, but it is often referred to as "rubber skin". Basically it's a spray can, which "paints" a rubber compound, used as a primer for paint, to avoid rust.
I was considering buying a can, and spraying the internals of my case with it, hoping that it would firstly give my internals a nice matte look, while also offering a minimum sound and vibration dampening effect.
Has anyone tried this and have any comments/suggestions/warnings?