Personally metal for the most part won't show 'noise' like the filter effects give. Such imperfections would be only be noticeable through a fine look over the piece, unless it's been subject to actual use wear. Even then the noise filter isn't what you'd see it as. I think the noise you're referring to is particles in high detail pieces other than the the object itself. Atmospheric effects such as dust particles or other elements of the atmosphere that make things 'fuzzy' in some respects.
A lot of the variety in the look to a metallic piece comes from atmospheric lighting. On top of the colors it absorbs, a large majority of it is reflected back, almost perfectly, causing a mirror like finish (if the image is distorted this is due to the surface being concave, convex, or imperfect in some other way). Remove the background and other elements, and you get a very simple looking object, assuming you could ever truly remove all objects from reflecting off of the surface.
I hope Venetia will correct me if I'm wrong, but I believe a large majority of the colors in the shadow comes from atmospheric lighting, you sit a red ball on a white table with a white backdrop behind the ball, and have this outside, there's a blue tint to the shadow of the ball because the table itself is picking up the atmospheric light as well, which is majorly blue, and reflecting this onto the shadowed side of the ball. Add to this the fact that the atmospheric light is hitting the actual cast shadow, if there was just the (blue) light from the atmosphere and no sun, the ball (or you and I) wouldn't cast a shadow (except for the areas where the light can't reach) because the light around the ball would be uniform.