4-20mA loop reading 9mA when transmitter is grounded

Hello!

I'm involved on a project where we use three flow transmitters to measure flow on three outlets through three separate pumps pumping seawater from two tanks. We use a Siemens S7-1500 PLC in a redundant ring-setup. Along with this we have a RIO with our A/IO modules. Our flow transmitters are wired (+24V -> transmitter -> PLC AI -> 0V)

If I physically remove the entire flow turbine and transmitter, I read 4mA in the loop, but once I touch anything grounded it will give a value corresponding to 7-9mA. All I have to do is touch the panel with the flange of the flow turbine and the current will increase. We tried grounding the transmitter and the whole panel its mounted on to the cabinet, but no matter what we do it's still showing the same behaviour. It's all connected with pipes and filled with seawater so it's grounded anyway. We also tried using a loop isolator power supply, but to no avail. I have used Arduino quite a bit and I remember that I would use a pulldown resistor when working with digital IO to avoid haywire values. Could it be the same for analog in this case? I guess maybe not, since the loop is never actually open, therefore no need to pull it down..?

I'm pretty positive we don't have a ground fault as our isometer is showing just fine and we get our power directly from a dedicated generator. We use a 440V to 230V transformer in our cabinet followed by a 24V power supply/UPS.

It's worth noting that when we have 0 flow, we get anywhere from 7-9mA. However, if we run the pumps at minimum capacity, it will show a value that's lower than 7-9mA. So some flow will give a lower loop current than no flow.

Thanks for any tips or thoughts.