Sump pump check valves stop the back-flow of water, but the BANG of the water hammer sound when these valves shut is loud.
The noise they make when they slam close can be heard through the house. Get one that is said to be “quiet”, “silent” or “soft close.”
Zoeller makes a variety of them that only make a comforting “whooshing” sound.
They will not be soundless, but they won’t bang either. Ask questions before you buy it for reassurance. I have used check valves that purport to be quiet even though they were not.
To install, remove the section of pipe under the valve, and stick a screwdriver into the check value to release the water above the valve. Then loosen the clamps (or cut), switch check valves and replace the pipe under the valve. If there is a shutoff above the check valve, you won’t have to drain the valve.
A home-size Zoeller quiet check valve is $20 – $30, and are worth the peace.