Replaced the overflow box. On the old box, the middle drain was too low, so you could hear the water entering the box. Since I sealed the old one in place before testing it, I had to order a new box. I tested all the drains raising the all three levels this time. Eventually I took out the far right one and just put a strainer there. It appears that the middle drain is the key. By making it taller, you do not hear the water enter the box. It is now "silent" as advertised. The difference was huge!
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