I used a pump similar to this one: Shurflo Smart Sensor Water Pump
you see more of the variable speed type these days - when using a small flow of water, the pump runs slower than when there's a large demand, in which case it'll power up!
Our's is fairly quiet as well - but I insulated the mount with lots of rubber grommets, and loosely mounted the input/output hoses as well...
Our pump is mounted in the rear bath, and you can't really hear it up front in the galley - we no longer need 'ear protection' when running the pump!
Water pump installations are one of my pet peeves in RV's! Our old Lance camper's pump sounded like Rosie-the-Riveter was working inside when it lit up!
I don't know why RV Mfg's can't devote more 'engineering' to the water pump system, and keep em' quiet! there's just no justification mounting the water pump to a panel that acts like a drum head to amplify the noise inside the living area!
I know it's a trade off trying to mount the various plumbing systems in a place where it won't freeze in cold weather, but I still believe there's more that could be done to keep the pump 'quiet'...