New Brakes but brakes still squeal when backing up Why

That all boils down to the quality of the parts installed and the installation procedure itself .. We're the brake *disc rotors* re-machined as needed? .. We're the brake pads OEM quality? .. Were ALL the *brake pads mounting hardware* inspected, properly lubricated and/or replaced as needed? .. We're ALL the *brake calipers* & the calipers *mounting hardware* inspected, properly lubricated and/or replaced as needed? Simply replacing the brake pads doesn't usually solve a brake squeal issue.

Brake noise is ultimately vibration and a few things can cause it. Did you lubricate the pins and slides? Sometimes applying a brake pad adhesive can help. This is a product sold in many different brands at every auto parts store that essentially glues the pad backing plate to the caliper piston. You must clean everything before applying and follow the directions. Also, what type of pads did you use and does the noise every go away after driving for a bit? Alex