My 60 gal build

[BlueAbyss]

Originally Posted by 04scoobysti

Usually I use a gate valve on the line from the overflow to the sump, and put it as
close to the sump as possible so i can tune the overflow and get rid of any unwated noise.
Most noise is just from too much air getting into the pipe.
My 2cents FWIW.

Aha! There's an excellent theory!

Is the noise coming from the water falling over the overflow, or from the pipe to the sump? More water moving through the pipe = more air being sucked through with it, like scooby said. Also, do you just have a plain bulkhead, or do you have a standpipe attached? If the noise is from the water falling over, adding a standpipe will reduce the height of the fall, and therefore the noise.