What 16ACE27 said...
There’s a number of ways to quiet noisy water pump.
1) look at pump while it’s running to see if hoses are knocking against any surfaces
2) add an small accumulator tank. It will make the pump run less, thus reducing noise
Seaflo Accumulator Tank - $35
3) water pump “silencer kit”. Although not needed if you can quiet existing hoses
Camco Silencer Kit - $24
4) Finally, rebuild pump with new diaphragm (parts are available on-line for half the price of a new pump) or change out with a whole new pump ($50-100 depending on brand/style)