Previous trailer, I did all I could to quiet down the pump. I put foam rubber under the pump and then screwed it down, but not tight, so it kind of floated. It helps a lot. Still make sound though.
Current trailer? OK, it makes noise, but who cares! It's part of the camper, and everyone in the camper knows it's a necessary noise, so they just have to live with it. Problem solved. Who cares! I'm not busting grapes again to quiet it down.
And? even with full hook-up sites, we always use our fresh water tank and on-board pump. I fill the tank from the available water source and turn off the source. Why? There is never any concern about over-pressurizing the camper's water pipes. When connected to "city water" you just never really know what the pressure is. So, to be safe, we just use the on-board pump, even at home in the drive way, where I know what my water pressure is.
Noisy pump? I'd tell everyone to just live with it or they can just go to a motel! Problem solved!