my 2018 prius sqeaks when i back up

Hello, You probably notice that it is worse when you press the brakes but goes away just as quickly. The brakes do get some surface corrosion when sitting outside because they go from very hot while driving to very cold at night. Condensation builds. If your brakes stop squeaking only while pressing the brake pedal, the wear indicator may be touching the rotor, but if they are just giving a little squeak as you press them in the morning, no big deal.