My 2004 cavalier back brakes make a groaning creaking sound?

when i was driving today, i noticed that my brakes made a groaning and creaking type noise when i braked quickly but steadily (i didnt slam on the brakes, the light turned yellow and i started to brake going about 40 mph). i just had my back brakes done not even a year ago (august of last summer). i had a wheel cylinder, 2 brake drums, and brake shoes replaced. does anyone know what it could be?