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.
"Blast and I'ma last yo, past all these Glass Joes and assholes who claim, like they be runnin' thangs.
I be gunnin those same jiggaz runnin late, to their fate.."