Water leaking to Grey tank while in city water

[rush2112]

As title states, I believe we have water leaking into grey tank for bathroom. I have opened the valve at the campsite and with no water turned on in the bathroom we see a slight trickle coming thru the slinky. If I turn off water at faucet it stops. Have water regulator on set at 45. Any ideas?.

FYI, just had water pump changed under warranty. Otherwise it's a new 2018.