Hhhhmmmm?
My system I mentioned above was my first time doing some with a reef ready tank. I had also posted several questions about asking for help to design it in a perfect way. I got slim to no help or answers.
As a result I made my first attempt. Being my first attempt I made a few errors. Gluing my standpipes together was error number one. Being lazy and not wanting to make new pipes was error number two. As a result what I did to compensate was I added air to the system. I added air to the system to slow the flow down because otherwise it gulped air and made a tremendous amount of noise.
Adjusting my air mixture fixed my gulping, but it still made some noise. Adding the valve helped me to alleviate the noise because it also allowed the water levels in my overflows to increase and that quieted my falling water noise as well.
I never said that my system was perfect. I know it wasn't perfect. I attempted to ask questions from the community to help me before I begin the project. I received zero feedback. So my system is flawed.
https://www.monsterfishkeepers.com/forums/threads/new-tank-with-sump-is-noisy.688806/
And this was my attempt to try to figure out the flow rates. So I could size my pipes correctly. Again maybe it's me, no responses. But boy oh boy, I'm getting a full on argument about expressing some of my ideas. In this thread.
https://www.monsterfishkeepers.com/forums/threads/help-me-with-flow-rates.689107/
But I can tell you one thing. I learned a lot. I was just conveying my experience the original poster to give him some other ideas to contemplate.
But let me say this about my system while it's not perfect it's not running at full siphon etc. etc. it is extremely quiet. There's almost no noise from inside the aquarium there is almost no noise from under the aquarium for the returning water to the sum, the noisiest part of my entire system is my Danner 1200 pump. I know I could get a DC pump that's quieter but I'm afraid of that pump because of some of the reviews. I do use one on one of my other systems that I have a back up pump installed on. But I'm not ready to have it as my only pump.