You gots yourself a weird one!
Any dripping sounds originating at eye-level and above are normally not waste water related.
There are usually no pressurized water lines above eye-level either.
The only plumbing above eye-level are the vents for the waste tanks. Normally they exit through the roof and produce near zero noise up there.
I often hear a dripping noise when on the toilet: Liquid refrigerant moving inside the fridge. We camp where it is REALLY quiet!
Now, it is possible that there is a waste tank vent (admittance valve) inside a wall somewhere. This could be the source of a wastewater drip, but the shower pan would flood first.
Try thoroughly flushing the grey tank and get the sensors sorted out (warrantee repair?). The level gauges are never accurate, but still they should have clue!
Also try and keep a rough idea of how much waste water you've generated.
TT 2015 19RD "TheJayco"
TV 2003 F-350 "Montblanc" - Housebroken chore truck
Sitting in The Cheap Seats.
And proud of it!