RV Repair: Water Heater, voltage side, becareful

Question
I have been hooked up for about three weeks. I have a 50 amp. hookup. When I woke up this morning I did not have any hot water. I have hot water if I use my propane. I have the switch on the 110 voltage side and the red light is on. When I opened up the water hearer cover I hear a light buzzing sound. I checked the fuses and they seem to be working because when I the fireplace and the water heater on the same fuze and the fireplace works. When I use the propane the buzzing sound goes away. I can't figure out what is wrong, Help please.

Answer
There is a relay that switches the elect on the water heater it is 12 volt ant some times when the element goes bad it will hum or just the relay in the back is bad becareful because there is 110 volt back there and it will hurt you



let me know what you find