IF you get excited and want to study this a bit more?
I can ignore lots of small complaints but some bug me more and get me to do something!
Are you aware of the interactive parts catalog that lets us look at things like the plumbing without doing too much crawling around?
You don't say which floorplan you have or early or late build but with that info in hand one might be able to go through the drawings and look at where suspect points might be!
I play with that section a lot here on the forum and now find it easy to move around. But it has a learning curve built in!
I did a quick look at one of the models and picked a few points where I might think water and pressure could get out without being noticed.
You may want to do a slow thoughtful check for yourself but some ideas that you might take a quick look at for leaks?
There is often a really, really, cheap little plastic "flap" at the water input port where you attach the hose. Basic little plastic disc that a spring holds against the rest to seal water from the pump pressure going out that hole.
If the pump action changes when you do something with the hose, is that showing the little disk is not sealing the hole right?
You can often see that little disk when no hose and you look in that hole! There may be a screen over the hole but I often take that screen out as I don't feel the need to strain the city water I use! Maybe a quick look or putting a plastic plug in that hole to test what happens would be worth the effort?
A second idea of where water might go and not be seen is underneath the RV where all those drains dump to the ground!
Those or the suction valve and tubing for antifreeze might let a dribble of water out in a place we might never look! Any drips showing underneath?
Congrats on getting the problem down to what is "passable" but if it still bugs, you might want to give more thought on some nice day!