This was always with Semi-Metallic pads though, which came with their own shims that you installed. Going back to OEM shims was the answer, perfectly quiet afterwards. Recently upgraded to Brembos up front, I had to use the shims that came with the pads which were the exact model of the pads I was using with the z32 calipers. I got no noise whatsoever with the aftermarket shims on the new calipers which is interesting. Still using OEM shims on rears.