OKay, its me again.
This time I thought hmmmmm. Use a multimeter. I set it from 0-600vac
and 0-600v dc and nothing showed all on the case, inside or outside.
I can stop the microphone hum just by touched painted, non conductive
pc case surfaces therefore I diagnose that there is not an earth
problem. I trust that I am correct however, I dont want to be wrong
in anyway so if you can just give your verdicts when you have a
chance, I believe that the matter can be closed and put down to
something else other than earthing problem.
bye