Are you hooked to city water and have your pump turned on?
Many times. espically if you use a "Regulator" of the cheap variety (roughly a 3/4" cylinder one piece May have a bright plastic grip on the female end) these are not able to deliver the GPM to the shower. So if you have your pump on it will kick in. if the fresh water tank is full of air. not water. Well it pumps air into the lines.
The solution is one of two things
1: Fill the tank. That way the pump pumps water
2: Toss that piced of junk regulator and get either
1: A Valterra Adjustable or
2: I use a 3/4 inch Watts or Zurin (I have both brands) with hose adapters. When new I can set them to 50 PSI Static. and then turn the shower on FULL and that needle does not even wiggle.. Pump will never run.
When they age and start restricting flow they can be rebuilt.
That said. I no longer use 'em.. the reason is I use method 1.. Fill the tank and then use the pump.. Long story as to way but the short version is it fixed a problem.. not with the rv but with the water.
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times