My sump pump makes a loud noise every time it stops pumping, How can I stop it from making this noise ?

Most "after turning off" noises from sump and ejector pumps are the check valve. My ejector pump gives a "thump" when the valve closes. There should be a check valve or water will be sucked back into the pit. Run the pump and listen at the valve.

Yup... most likely the check valve as ma0641 said.

They make a QUIET or Silent CHECK VALVE... available at home depot or amazon.com... simply swap the existing one out with the newer, quieter version... should help!

Mark

As advised above, check valve is most likely at fault. What happens, faulty check valve doesn't hold water, water keeps seeping through the valve, and every time it does, it vibrates with the flopper by lifting up and closing it - in quick succession. That is the noise you hear.

Milo