Dealer fixed the issue with water coming in from the onboard tank. According to their report, filter was blocked. BS, the winterizing suction tube worked fine and the shut off valve is now in the system with hose clamps... so that was at least removed by the dealer.
Now, I've got water hammer so bad that something is likely to break. Found no o-ring to seal the filter to the pump, added an o-ring. Did not change the behavior.
This may be an important observation, while the water hammer is undergoing, the LED lights are flickering.
It's 150 miles one way to the dealer, and I'm more than a little frustrated.
