i had the same problem , and initally thought it was the heat plate , took it again to the dealer today and they finally found the problem. the caliper is touching the rotor head , causing the squealing, the spacing between them is much much smaller than required . they still dont know how to fix it . might replace the caliper or the rotor head to see if they can give more clearance between them to avoid touching. both rear brakes have the same problem 3 mm clearance , the front ones are fine they have 12 mm clearance.