Solid, I appreciate it.

I was originally tapping into the factory becker's brown wire ground. I've now installed fresh grounds to the chassis for each component as good practice.
I doesn't appear I have any ground loops. Also, from what I've read about ground loop isolators, they do a number on the low end part of the signal.

Definitely appears to be the charger itself. Have ordered a variety from amazon to see if one does the trick...

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1981 240D 4sp manual. Ivory White.