problem with audio when it is placed in a multi-track session (gyrating gain on background music)

I used Adobe Audition to extract the audio from a CD. The audio features narration with background music. When I open the extracted audio file by itself, it plays perfectly. But when I add the file to the multi-track session, the narration sounds fine, but the background music has an odd gyrating effect in the periods where the narration pauses.  It sounds like the gain on the music is gyrated up and down.  If I export the session, the effect is baked in to the resulting file. Both the audio file and the session are set to 44100 Hz stereo. 

Any help would be greatly appeciated.

Paul