Stray current to me is everywhere, but in most cases it does not result in stray voltage since the resistive paths are low enough.
With that said, most stray voltage is the result of normal current on intended paths, yea I know this goes against the grain, but think about it, most difference of potential is cause by normal current on feeder neutrals, service neutrals, and primary neutrals (MGN'S), are these all carrying normal current?
the stray voltage or difference of potential is the voltage drop across these paths through these neutrals to which most grounding is bonded to.
Now for the shocker:
GFCI's will not protect a person against shock if the voltage on a system grounding is elevated from earth because of the voltage drop on the supply side neutral!
Ground rods do little to nothing to bring this differance of potential back down.