Picture by Doug Brummett - uses same design but hooks into a bulkhead added to overflow box.
If I were to implement this design, I would recommend that you place the bulkhead opening higher than pictured here. This will help reduce the sound even more by raising the water level height in the overflow box.
The design as pictured here also requires a lot of room behind the tank. More than most people usually have. I would suggest you drill the bulkhead hole on the side of the box instead.
The blue item on top of the pipe is an air-valve.