Welcome, just a couple things you can do for the overflow. From the pictures the water does look a little low in the tank. The valve on the return line can be closed a little to achieve a full siphon and that should cut the noise down. You could also re-do the overlow and look into the bean-animal or herbie method. They also make silencer caps for the overflow pipe that may help. I also noticed that your ATO float valve is in the same chamber as your skimmer. The ATO float or sensor always needs to be placed in the return section of the sump. This is because the first chamber to be affected by evaporation or water loss is the return chamber.
It would also help to see more pics of the overflow pipes to see if we can see anything that looks off. Your skimmer also appears to be skimming very wet. You should adjust the skimmer so the bubbles are at the very start of the skimmer neck. The skimmer can also be raised using a flat rock, pvc or they make skimmer stands to raise the skimmer more in the water. This will lower the water level in your skimmer, giving you a more consistent and drier skimmate.
