...as it may work.
1) Double click on the speaker icon in you taskbar.
2) click "Options" in the menu
3) choose "Properties"
4) click the "Recording" circular button
5) put a chackmarks in all the square boxes you see in the list
6) click "OK"
Now play something with is quiet enough that you can hear the hum clearly. One by one mute the Recording options. You may well find one which is not muted, and humming away nicely. If you go through them all, and the hum is still there, do the same thing as above but at #5 choose "Playback", and do the same thing again.
All those sound channels and options aren't by default configured for every sort of connection or device.
I am trying to hook up my PC to my home stereo. I have a cable with a stereo mini plug connected to the speaker out port on my audio card and a pair of RCA plugs going to the tape monitor inputs on my home theater receiver. When I try to play music through the home theater receiver, I get music but also a pronounced hum. My cable is 25 feet long to get from one room to another, but a test with a MP# player produced hum-free music over the cable to the home theater receiver. Anyone have a suggestion for where this hum comes from? Is it because the speaker oout levels are incompatible with the tape monitor inputs? If so, do I need a new card with line level output or can I use a different input on my receiver to match the levels from the audio card?