Water HAMMER or pump hammer
The first.. You turn on the faucet and it's good but you turn it off and WHAM.. This is caused by the water hammer absorbers (Look like a short pipe going nowhere) filling with water... NOW not all RV's even have these because the lines are not long enough to cause water hammer.. IF you need an explanation as to the cause.. Well I and Newton do have one.
Pump hammer.. The pump is a "Jack hammer" type device and it will hammer the lines from time to time.. Two things.. Sometimes the manufacturer runs PEX all the way to the pump. puttin a "loop" of flexible pipe in either side of the pump. fixes it.. But I have that loud hammer frequently and my RV already has flexible lines to the pump (I know I checked)
Time will fix it. I do not yet know the cause. I know sometimes if I run out of water. it gets LOUD and then after I FILL it will stay loud for a while. then it simply goes away.