I just purchased a song to add to a brief IMovie clip I made. When I played the clip back and tried to play on Facebook as well the sound was all scratchy?? Is there a specific file I should be using from those downloaded that has the best quality? Am I simply choosing the wrong file? https://youtu.be/UzOmtiRQ1eI
Have you adjusted the volume of the music in iMovie? It should work fine with a MP3 file but you could also try the WAV file.
It must have been some randomly corrupt file. I tried it again and it worked fine this time. https://youtu.be/gmwIWQJWTWg