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.
"I call suffering my brother. I love him like my mother. We look out for each other, we'd die for one another.
I fight, I brawl, I feind for this. I scrape, I crawl, I bleed for this.."