My speakers have developed a 60 cycle hum. If i turn off the speakers the hum stops. If I plug in ear phones into the front ear phone jack I do not get the hum. If I plug the speakers into the same ear phone jack I get the hum. I have tried moving the speakers to different locations, no change, still get hum. Reversed plug in power supply, no change, stil get hum. Do I just need to replace these speakers?