[Sirrotica]

There may be a crack that has developed across the sweep area of the drum surface due to overheating the drum, as the brakes hit that crack it may be making a noise.

One other thing I have seen happen with drums that have been turned is that if they were turned on coarse feed, they actually develop a thread inside the drum. As the brakes are applied, the shoes lift off of the backing plate, and the hold down springs snap the shoes onto the backing plate. Working at dealerships I have seen it on new cars, as well as in a regular service garage dealing with brake noises..

Turning the drums on slow feed with a light cut will normally get rid of the thread, and the snapping noise.