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.
"So I'm drifting away like a feather in air, letting my soul take me away from the hurt and despair.
So I'm, keepin' it vertical forever elevator, riding the escalator to something that is greater.."
Cypress Hill x Rusko - Lez Go (Monista Remix)