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.
"We've come a long long way together. Through the hard times and the good.
I have to celebrate you baby,.. I have to praise you like I should.."