Please thank you. It's very "slurpy". . Could be normal. Idk. I literally bought the sump and overflow on a whim with a pump super cheap and headed to home depot. After a bunch of saltwater in my mouth and on the floor I got it going until I ran into trouble and started this thread ..If you need to regulate the water going into the tank you'll put the valve on the line going from the pump back to the tank. If you have room in your stand, under the tank above the sump it will be out of the way but still accessible. DO NOT restrict the water going into the pump by putting the valve before the return pump. Can you determine where the actual noise is coming from? I'm assuming it's a sucking or slurping noise?
