2019 Porsche Macan Brakes

THE ISSUE IS THE SQUEAKING OF THE REAR BRAKES WHEN BACKING UP. THE WOULD HAPPEN WHEN THE CAR HAD BEEN DRIVEN. THIS HAPPENS IN COLD OR HOT WEATHER. A FACTORY DEALERSHIP HAD LOOK AT THE ISSUE BUT FOUND NOTHING. THIS PROBLEM STARTED WHEN THE CAR WAS ABOUT TWO TO THREE MONTHS OLD. I ALSO HAVE A 2020 AUDI Q7, AND IT HAS ALMOST THE SAME ISSUE WHEN BACKING UP. HOWEVER, IT DOES MORE IN THE MORNING WHETHER THE WEATHER IS HOT OR COLD. WE VISITED AN AUDI DEALERSHIP BUT THEY FOUND NOTHING. A SEPARATE COMPLAINT HAD BEEN FILED UNDER MY NAME AS WELL. BOTH CARS HAVE THE SAME 3.0L V6 ENGINE.