A brake pad shim is used to isolate the pad from the caliper piston to prevent noise.

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Brake noise comes from vibration transferring between the pad and the caliper piston. A brake pad shim provides a thin isolation layer between the pad backing and the piston surface, dampening those vibrations and preventing the pad from rubbing or resonating against the piston. This damping action is what helps stop squeal and rattle during braking. Shims are usually metal or composite and can be bonded to the pad backing or placed directly against the piston, depending on the design. So the statement is correct because the shim’s primary purpose is to isolate the pad from the caliper piston to reduce noise.