My experience is that ground hum most often comes from your CATV system. It's not always the culprit, but it's what I'd check first. Disconnect the CATV wire from the wall and see if the hum goes away; if so, get a ground loop isolator and put it between the wall and your componentry.

I'd avoid defeating the three-prong plugs on the basis of safety. If your equipment were meant to operate with two prongs only it would have come with a two prong plug.

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Matthew J. Hill
matt@idsi.net