Consider one of the variable speed water pumps from Flojet or Shurflow. Not cheap, but very quiet. I have had one in 2 different motorhomes and am very satisfied.
Edit. Going from memory, the variable speed pumps are around 2 inches longer than the OEM versions. This was an issue on our '95 Trek, but not on the '99, so be sure you have additional room.
George Schweikle Lexington, KY
1999 Safari TREK 2830, FMCA 190830, Safari International chapter
1995 Safari TREK 2630, 1983 Winnebago Chieftain, 1976 Midas Mini