Song suddenly turned crackly

Created a song in around 5 hours, very happy with it, just finished it and was listening to it one last time when it started crackling awfully. Every sound played was robotic and extremely crackly - not like CPU crackling. It happens occasionally on my PC, when the sound is run through my audiobox. To stop it I need to change the number of samples in my audiobox control panel, which usually fixes it. However, every other sound now works but the song sounds the same, just as crackly. The autosaves sound the same. The files in the media folder sound fine however.

Exporting a mixdown of it results in a perfect file... Any ideas?