When I had a 72bow front with built in overflow I stacked sponges on the inside of the overflow wall so the water went through those instead of cascading down the side (which is where the noise is coming from) Much quieter. Mine wasn't just a hole in the bottom though. It had a stand pipe with notches cut in it, covered with a round pre-filter sponge. It still needed the other sponges to keep it quiet though.