I got a piece of steel from a scrap yard and cut it so I could mount it at a 50° angle. Made a wooden box around it and filled the bottom with about 2" of sand. Used an old door catch at the top to attach cardboard for holding targets. Behind the steel plate I stuffed an old foam rubber pillow to deaden the sound of impact some. The pellets hits the steel and whats left of it ricochets into the sand at the bottom. Not a single pellet has left the trap yet. It's not silent, but it's far from noisy. Total cost less than $25. The toughest part was cutting the steel with a Saws-All. 
