2003 Chevy Cavalier

I own a 2003 Chevy Cavalier with 79000 miles. It's an automatic, 2 wheel drive car. I recently had the brakes serviced in order to pass inspection. The mechanic installed new brake pads and rotors for the front, and cleaned and adjusted the back brakes. I began to hear a squeak from around the front end as soon as I drove it off the lot. I have returned on 2 occasions and they cannot find anything wrong with the brakes. At this point, all they did was lube, clean and adjust them. Today, I went to drive the car and it seemed to be stuck when I began to accelerate. There was a loud "pop" and the car began moving. Now the noise seems louder. Is there anything that can be done about the brakes? Is the "pop" noise somehow tied to the brakes?