I've done several things to make my system almost silent. Starting with the overflow. I went to a herbie which is silent if you get it dialed in right. That made a huge difference. I also made a cover for my overflow, that quieted the falling water noise into it. In the sump I terminated all pipes draining into the sump below water level. That eliminated any falling water noise into the sump. In the sump I used dc variable speed pumps for my skimmer and return pump. Good quality pumps like these are almost silent. I also have a cabinet which I made. With doors on the front and a totally enclosed back it muffles any noise from the skimmer and pumps. I had to put a small exhaust fan in the back of the cabinet to remove humidity so I used a small computer fan that is silent. My tank is in my office and I work from home so I couldn't have Niagara falls going in my office all day. About the only noise I get is a small hum from my return pump that I have to stop and listen for to know it's there.