I've noticed on sites like rockauto there are rotors for sale that are described as quiet. Supposedly there is a type of iron (called "Gray" iron) that has a different microstructure that is less prone to high-frequency brake-squeel noise, but this type of iron is supposedly what most or all rotors are already made with. So is this true? That you can count on your standard white-box, no-name brand of rotors that might cost you $20 - $30 a rotor is already made using the most appropriate type of iron, this so-called "Gray" iron, and that anything labelled as "low-noise" rotors are just throwing that term in to extract a few more bucks from the price? (This is not about whether or not a rotor is cross-drilled or slotted, so let's not take this thread on that tangent). Also, I've noticed that there are some rotors that appear to be black in color - not just the edges but the entire rotor. I think these are described as being zinc plated - presumably the plating gets worn away on the rotor surface in contact with the pads. Anyone have any experience with these? Do the areas of the rotor that are black *stay black* over time and hence they don't rust?