The metal on metal is probably your brake pad wear notification that it's time to replace them. The rotors (metal discs the calipers clamp on) will rust slightly in the middle and I don't think it's a huge deal unless it's a lot of rust. Typically, the rust doesn't build up where the pads make contact though.
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Zack
FI catback, HFC, and Start Button - Z1 Intake - Nismo S-Tune Spoiler - PasswordJDM V2 Shift Knob
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