Franco7 â€“ I have a 404 too and using on my planted 72 gal
I cannot tell ii it working unless I put my ear next to it.
As per you problem, my take is.. that because you the air wand under the filter intake, air bubbles get sucked in with the water. This causes all the noise.
I would move the intake where no air bubbles get suck into the intake and then the 404 will be wispier quite.
Keep us posted on ur progress..