I assembled a mb/cpu case etc... combination. I have done this many times before. When I shut down Windows the PC does a soft power off as it should with an atx case/ps. I can hear a humming coming through the speakers on my system. If I unplug the speakers from the sound card and touch the tip of the plug around the area of the power supply I can hear the same hum. If I turn off the power supply completely it stops. Do I have a bad power supply? Is something not grounded properly? The system works fine it is just kind of an annoyance.