I just bought a certified preowned 2007 Lexus ES350. When I back up, the brakes make a loud sound like a french horn being blown. When I tell the dealers, they laugh it off, and say it happens when the brakes are wet, and that it will stop once they dry. It does it all of the time. They obviously are knowledgeable about the problem, but have no intention of fixing the problem. Does anyone know more about this brake situation? Thanks