Overflow

[GMGQ]

Wrap some Gutter Guard around the intake box of the overflow. Cut it to size to wrap around 3 sides of the box, then fold it at the corners, and zip tie it around the back. That should help with preventing fish and other critters from going in there.

For the sound, assuming your overflow box has 2 drains, you can add a gate valve to one of the drains, where it exits into your sump. Just choke back the flow so that you doing get that "toilet bowl" effect from that drain line. It should be 100% silent.

Then cut a piece of PVC to make the other drain taller. This one would be the Emergency drain, in case the main one gets clogged up.