I would wager that this has something to do with the step down transformer.
Ken, this is highly likely...Due to the transformer in the the mix this, in of it self could also be the source of the ground loop as this is a new device, and does not address the grounding of that circuit...
How did you wire the ground? If you could post a schematic of how you wired the outlet with the transformer that would help. At this point everyone is hypothesizing as to what you did...
lol... this is what i was just writing as you posted the solution..... oh well!!
With this being said, i would bet the source of your ground loop is the wiring of the outlet off of the transformer.. Again, if you can post a schematic we could help eliminate the ground loop.....
