Have you tried putting 'cheater plugs' (lifting the ground) from all but one three pronged plug? If the buzz/hum goes away, you are good to go, since ALL components that are connected (via interconnects) to the grounded component will be safely grounded. Check out this Michael Elliott web site for more info:
http://www.altavistaaudio.com/hum.html
Hope it is as easy as that.
http://www.altavistaaudio.com/hum.html
Hope it is as easy as that.