fmt_biker and 009jim, do you happen to have grooved rims ?
From my experience, the metal chips stuck in the brake pads come from the rim itself, and 90% of the time its a factory grooved rim (like sun UFO, for example). I saw it on many kinds of brake pads, and when it happens the brakes produce an awful noise and (as you already mentioned) deteriorate the brake performance. If you pry out those metal chips the brakes will get back to its original performance, but only for a short period of time (until new metal chips will get stuck).
*my very first message
excuse me for any grammar/vocabulary mistake, as English is not my first language.