Cheapy electrical cords dont have a proper earth and i hope its not the actual wall mount that has a shady earth.
The best way to test this is to move your pc and plug in directly into a wall socket . IF it goes away its the extension cord or multi plug . If not it could be the wall socket.
The best way to test this is to move your pc and plug in directly into a wall socket . IF it goes away its the extension cord or multi plug . If not it could be the wall socket.