Brake Whistling Noise problems of the 2014 Buick Encore

The vehicle was purchased new in November 2013. The vehicle has been serviced at a local dealership 6 times since the beginning of March for problems with the brakes. At slow speeds (between 1 and 25 mph) when the brake pedal is depressed or released a whistling, whirring, and grinding sound generates from the front of the vehicle. (the noise started 4 months after the purchase of the car. ) the noise is so loud that is can be heard over a radio set at sound level 18 and disrupts conversation in the vehicle because of the ear piercing noise that is produced. A brake hose, the brake vacuum pump, and front pads and rotors were all replaced. The grinding sound has stopped but the whistling and whirring sound continues and now gets louder the more the brakes are used and the more time that is spent in city or stop and go traffic. Today, while stopped on an incline in traffic, the whistling and whirring sound started and the brake pedal started to move lower to the floor. As the whistling noise continued and became louder, the brake pedal became softer and moved closer to the floor and the car started to roll. Reapplication of the brake pedal resulted in the same response of the loud whistling noise and the car rolling forward. If the traffic light didn't change the car would have rolled into the vehicle in front of it.