Try re bedding them. It's helps a a lot with these pads. Mine were toast after two years on my old 330ci. I too had a lot of metallic noise with those pads and zimmerman rotors. I recall actually like those cheaper akembono pads over the HP.
"Driftin' away like a feather in air. Letting my soul take me away from the hurt and despair.
keepin' it vertical, forever elevator. Riding that escalator to something that's far greater.."