Does water boil inside the water heater?

An electric S&B house water heater does the same thing. I occasionally hear mine from the upstairs bathroom. The boiling is on the surface of the element, but the contents of the whole tank is not boiling. If it did.... and the poppet didn't pop-it, then there's be a big mess.
A house water heater is generally set to 115° or a bit higher to reduce scalding hazards. However, due to the small volume of an RV WH, the temp is around 160°. This is mixed down with cold water to workable temps, but there's always a risk of scalding. 117°+ will scald; this is one of the reasons natural hot springers carry thermometers - I've measured water coming out of the ground at 180°. It cannot be finger-tested...

A failing electric heating element will cause noise when water can leak into it. Even a new element can make a slight hiss, if yours recently got much louder you should pull it and have a look. Replacement is low cost and takes less effort than all of our typing.

I posted something similar a few years ago and the general response was that I was crazy. So welcome to the club! In detail, I didn't hear the slow, large bubble boil as from a pot on the cooktop, but rather fast moving slow bubbles, that I assumed were right at the surface of the heating element.

Sometimes mineral buildup on the electric heating element gets a little noisy as it expands and contracts while heating the water. Assuming the safety devices are working properly, the water should never boil.