Had the same thing happen on my Vegas. Think it was some grit in the check valve of the pump. Was on city water and I heard water running outside. Went out and looked and water was flowing g out the overflow of the fresh water tank inlet.
Shut off water. Turned on pump and ran it for a minute. Turned city water back on and drained the tank. Never had a problem again.
Figured a piece of grip in the check valve was allowing g water to flow through the pump (backwards) into the tank.
Ed & Bev Felker
Retired USAF Col and retired Nurse
Traveling with Lily & Bella ('Teddy Bear' breed)
2015 Vegas 24.1 (E-350)