I would use the oscilloscope wherever you are testing for voltage so that you can see what the waveform and frequency are.
I would also check the current in AC and DC to see what that shows.
A signal generator would also be helpful to verify which line is responsible for the stray current.
I would also check the current in AC and DC to see what that shows.
A signal generator would also be helpful to verify which line is responsible for the stray current.