1999 Chrysler Town and Country noise when braking

A friend and i recently changed the rear brake shoes on this van. Completed the job and all seemed well. My friend insisted that one of the brake drums should be replaced, so 2 weeks after the job was done, we took the worn drum off and replaced it with a new one. Then we adjusted the brakes. Since then, last Sat, when braking you hear a definite knock, knock, knock from that wheel. The van is stopping fine, no bouncing felt in the pedal. I do not hear it if traveling 50 to 60 and make a hard stop. Noise is only when braking and most noticeable at slow speeds. Any ideas?? Thanks, don.