The engineers say the difference it made in their equipment noise is like night and day.

Yeah but this was a video problem. I never really thought about the difference a ground loop could make to the picture quality/frame sync signal.
I did some work in audio in a studio where a 'black' generator sent a signal to every editing machine in the studios. just to keep the same sync rate. we never had any real sync problems, even with finnicky machines. but we could have!

Murray 06000047
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