Final Cut Pro Audio issue :S

Basically, I am editing a montage for a music film, and I lay down the audio track 1st which is an mp3 and I begin cutting the footage to that, but when i stop and play the audio track from the begining it is not playing the track normally, it is playing it then the track suddenly cuts to another portion of the song as if i have sliced the track and joined two completely different parts of the track together. The track which I layed down has not been edited in any way its literally been dragged and dropped onto the timeline from finder and it plays back smoothly when I play the mp3 in itunes, but for some reason FCP keeps making the track jolt so now my montage doesnt make sense rhythmically!

Anyone know what the problem could be?

Thanks guys