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.
"This vagabond life can I transcend? To give up sleeping beneath the stars. Life on life’s terms does not pretend.
This journey fades as I near the end. The long sleep under Venus and Mars.."