MainerBob wrote:
This is the OP and I thank all of you for your helpful info. Having shut off the electric and still getting the noise I have concluded that it is the check valve. I have good access to the back of the heater so next time we are someplace with RV parts I will pull it out and replace it. I'll also look at the anode. Right now we're in Terlingua, Texas where they think an extensive assortment of RV supplies is one pack of AquaChem toilet paper. Have a great holiday, y'all.
Bob
Instead of a new check valve that can cause problems again just remove the internals of nipple on WH tank (check valve) and install a shut off valve (1/2" available at any hardware store)......no more check valve problems and easy to isolate hot outlet side when bypassing WH to winterize....IF/when you need to winterize.
Anode rod only used on Suburban Brand. It's there to protect the porcelain lined steel tank from corrosion/deterioration.