Wierd brake problem

I have a 99 Ram 1500. It has rear drum brakes. I noticed today that, each time I press the brake pedal, I hear a buzzing sound coming from the left rear wheel area. It stops when I release the pedal. It almost sounds like a buzzer going off. This is very odd. Any ideas?

I would jack it up and pull the wheel then pull the drum. I think a spring is rubbing against the drum causing the noise. Look for rubbing bright spots.