Rust can grow behind the caliper bracket channel.I would use a file and sandpaper to clean that channel because the hardware could pinch the ears of the pads and get stucked…they will not slide properly.I usually sandblast the whole bracket until its completely free of rust. As for the noise,your pads need a break- in period before they mate to the surface of the rotors. Some squeeking and light grinding noise might be heard during that time.