IMovie audio sync

I’ve got a audio file that syncs to the video when I’m playing them separately (audio through itunes and the video through the mac’s quicktime player) but as soon as I add them to iMovie, alongside another video (which is just a different angle of the same take) the video starts drifting out of sync.

I’ve created another project with just the audio and the problematic video and the audio sync was fine but as soon as I add anything else, nothing syncs up