I setup a 55 gallon aquarium with a 700 gph overflow kit, a 10 gallon sump, and a mag drive 7 pump. The overflow is pretty quiet, but the water running down pipes makes a lot of noise. I even tried a mag drive 3 and it's still pretty loud. It doesn't sound like a gurgling sound just the sound of the water running down the pipes. I've adjusted the air line tube and it makes no difference. The drain line ends about 2 inches below the water level in the sump. I was considering increasing the size of the pipe after it comes out of the bulkhead to 2 inches and using a sanitary tee to setup an external durso and then having the drain pipe end as deep as I can in the sump with a reverse durso at the bottom. I'm also using a filter sock for mechanical filtration and to catch air bubbles. What do you think? Thanks.