I know a lot of homes(older) in the South did not use the regular three wire outlets with neutral, hot and ground. Instead they used the neutral as ground(there is no actual ground wire) I have run into problems actually grounding and/or installing stuff around here. Check the wire and see if it is 2 conductor Romex or if it has a metal shield on the outside going to your outlets. If it has the metal shield, you can use this as a ground.
Try(if you haven't already) rotating the plug 180 degrees on one component at a time and see if the hum will stop. I doubt you have the standard sockets with the large spade small spade opening unless they were upgraded at some point. You can use a cheater plug if need be. You may have a polarity problem with one piece of equipment.
Also, if you have any variable lighting---turn it off. It feeds back on the line in these homes.
Try(if you haven't already) rotating the plug 180 degrees on one component at a time and see if the hum will stop. I doubt you have the standard sockets with the large spade small spade opening unless they were upgraded at some point. You can use a cheater plug if need be. You may have a polarity problem with one piece of equipment.
Also, if you have any variable lighting---turn it off. It feeds back on the line in these homes.