a plumbing contractor to replace an anode rod. You got WAY too much money.DIY or ask some other camper around you. If you have a RV you must know how to fix things or you will be in the poor house in short order. Nuf said. the noise could be the water boiling off the element. Happens all the time in electric heaters at a home. No differance, smaller tank. Some (Attwood) don't have anode rods nor does mine (Surburban) as I took it out in 2007 and installed a 3/4" brass ball valve in it's place. Can blow out the crud in seconds now if needed. Household water heaters have an anode rod and no one would ever think of replacing them. Think about it. Have any on you reading this even thought about it. Be honest now.