Randy, same here- no harm was meant in nitpicking the terminology- just trying to be clear. I agree, you are getting good advice from your co-worker.
Quote:
MDrew said... I had thought there may be some stray voltage or inductence on the neutral leg from the lighting circuit if they shared the same neutral. You said they don’t
I am still unclear if this is true- because of the confusion we may have had in the terminology. I know that you didn't believe it was the lighting circuit because you turned off that breaker and still had the noise, but I would guess that the white wires from both the 20A HT circuit and the 15A light circuit are indeed connected back to the same Neutral bus, and therefore shared. They should be really.
I would agree with you and your co-worker, try the ground isolation first (use a cheater plug so you don't have to physically disconnect the ground). If that solves the issue however, investigate further into the cause as removing the ground should not be a permanent solution.
Good luck Randy, we hope you get it solved and just want to be of help. 
Dave.
