I spent many hours and lots of foam , rubber mounts, and was still very loud ! One day I tried something that makes no sense but it works It only took me 1 1/2 years. First thing is to remove your kitchen and bath airators and clean and inspect, my kitchen one had 5 count them 5 screens in it and both airators had white plastic in them, #2 clean the clear bowl on the suction side of the pump it also had white plastic in it.#3 make sure your water heater is bled of all the air, Here is were it gets strange 1st turn off the pump and open the tank drain until you get a steady stream.( the pick-up for the pump is on a T with the drain ) then turn on the pump and take out the airator in the kitchen and open the cold water all the way and let it run awhile, shut it off and then the hot stand back there will be lots of water then go to the bath and due the same thing. Re-install the airators and try it again. I dont know why but this quiets my pump down to a purr !!
and I don,t wake the hole campground when I run water. I do this at home so I can drain the gray tank and re-fill the fresh water tank you will use several gallons of water. It may not work on yours but it,s worth a try. Also be shure to bleed the air from you shower and outside shower.
Good luck
Dale