"Robert Morein" wrote

You are getting way too complicated dragging Maxwell into this. Not that
that is wrong but is way too much analysis here.
You need two conductors for any single phase AC voltage. A third just
screws
everything up.

Bret, the above is the explanation for the definition and cause of hum
loops. It's not "too complicated"; it is simply the essence of the
problem.
The easy solution, most of the time, is to
use a power line conditioner with isolated
transformers. Over the years I've found
many electrical outlets which are improperly
wired. Having open hot, hot/grd or hot/neu
reversed. You assume the risk to your
equipment when you use a cheater plug
under those conditions.

And finally, there is no easily available
method to determine the quality of the
ground wire at the outlet. Maybe you
should use that huge intellect of yours
and invent one.