Loud sump check valve
You only need one check valve on the line, but some people will leave the old check valve in place if they don't have the parts to do the job correctly. The newest one should be left in place and the old one removed. Now, yes they do make a "SILENT" check valve. Look for one called 'The Silencer'.
The flapper is spring loaded just slightly closed. A 1/3 horse pump will overcome a 10 foot head plus the spring loaded flapper with no problem at all and generally you will not hear the valve "thump" even if you are within 6 inches of it.