Wow, you've hit one of my pet peeves with RV's we've owned/used over the years...
Why RV manufacturers haven't addressed this issue better is beyond me..!
Many mount the water pump to any convenient surface, usually a cabinet panel that act like a sound board or drum head to amplify the sound to an obnoxious level..!
Even a small amount of 'engineering' devoted to this system would result in much less noise;
1. flexible hose on input & outputs of pump - perhaps with a 'loop' - with hose clamps to a SOLID surface...
2. flexible 'feet' for the pump, designed with sound deadening in mind...
3. mount pump to a SOLID surface that will NOT transfer sound to nearby panels, etc...
4. variable pressure pumps that operate at different speeds based on demand will keep noise to a minimum for small flows...
5. allow enough space for the pump installation so that hoses won't rub or bang against nearby panels when pulsing...
Initial design of the water pump system for noise isolation from the start of manufacture - instead of the 'bandaide' approach of sticking the pump in some leftover space - would go a long way to cure this matter ..
We had an older truck camper that sounded like a motor that was about to throw a 'rod' when the water pump came on...
This issue reminds me of a train trip we took, back in the mid 1908's from Mazatlan, MX up to Guaymas, MX, an overnight ride... We were on the '1st class' train that consisted of old Pullman coaches from the 1920's & 30's...we had assigned seats that were directly above the diesel engine mounted on the undercarriage, that was used to power the air conditioning...
We noticed a slight 'vibration' as the trip began, and began to think it was getting louder a we progressed - was it just us, or was this just 'Mexico'...we noticed a couple of crew members outside our windows pointing and discussing something during a stop...
Our slight vibration was increasingly becoming a rear 'thumper' of a noise ALL NIGHT LONG... the train was full, so we didn't have anywhere else to sit...When we were about 30 mins from our destination, we heard a loug 'bang' as the engine finally threw a rod through the block and the ensuing silence was GOLDEN...! Oil was still dripping from the engine under there, as we got off the train that morning - what a trip - glad we had our own cooler with beer & tequila to ease the pain...!