[R-390] ground loop solution

[wli]

Firstly, thanks to all who offered opinions and advice re my problem. To reiterate, the hot and neutral AC supply lines were not crossed. The 3 to 2 AC adapter was put away in my toolbox. 

What I did do was get a small audio 1:1 isolation transformer advertised as a *ground loop isolator*, and said to have wide frequency response. It is  sold in car stereo shops for around $20. 

It worked eliminating 95% of the annoying noise.

Thanks

W. Li