Make sure you do not have a line output connected to the computer's Mic input. A line output must be connected to the Line input. USB audio devices with a line input
are available if you have a laptop that does not have a line input.
Make sure the input jack is not set to Microphone mode if you are not using a microphone. Use the "Sound" item under Windows Control Panel or any custom software incuded with the audio hardware to change that setting.
Reduce the recording volume in GoldWave and on any external devices.