To cure my "water falling noise" I went very basic. Instead of having the water fall into a pipe and crashing into the water that is standing in it, I got rid of the pipes and connected a 3' flexible pool hose to my bulkhead. The flexible hose gently bends from vertical to horizontal. As it gently bends, the water gathers and gently slows down. No crashing, no gurgling, no noise.
My overflow is just a plain piece of pvc, open at the top, with a sponge on top of it to keep snails and junk out of my sump.
Be aware that the brand new hose gave me a lot of bubbles for a few days until the walls coated over. Now, there are none.
I also found that by making very slight changes in the bend angles, "angle of attack", and how it twisted and turned I could take it from relatively quite, to almost silent.
Just another option. . .