adding a song to iMovie duplicates itself
After I add the song to my iMovie, it starts to play and then a second later it starts again, therefore duplicating the song. How can I fix this.
iMovie '11, Mac OS X (10.6.7)
It sounds like you are inserting the song twice, or possibly duplicating the music you've added to your project. If your method is to drag a song to the background area in your project (creating a green background), it may be better to use a different and more manageable method.
Drag and drop the song directly on top of a video clip (not to the background), approximately where you want it to start. Upon releasing the mouse button (or whatever you are using), a narrow horizontal green bar (ribbon) will appear beneath the video track, representing the audio track you have inserted. This track can be dragged anywhere within your project. If you wish to delete an inserted audio track, click on it so that it is enclosed in a yellow border, then press the delete key on the keyboard (alternatively, right-click on the track and select Delete Selection from the pop-up menu, or simply select Edit>Delete Selection from iMovie's menu bar).
Hopefully I haven't misunderstood what is happening with your audio. It's not something I've seen or heard about before.
John