Excellent suggestions by Larry. Also, are any connections present that could cause you to be listening to the same music via two different signal paths at once? For instance, are line-out and line-in both connected to some external device, such as some sort of recorder, that may be passing its input signal to its output? If so, you need to mute line-in in your volume mixer software when you are not listening to that device.
Regards,
-- Al