Why does my speaker keep buzzing?

Check your audio cable. Is it plugged into the audio OUT (green) port and not the MIC (red) port or the IN (blue) port? If so, plug it into the OUT (green) port. If it is plugged into the OUT port already, then it's possible that the wire is frayed and you should replace your stereo speakers. If that doesn't help then you might want to get a new sound card or replace the existing one.