iMovie Audio Error when Exporting

I am hoping someone can help me.
I have been using iMovie for ages and have never had any dramas until now. I have created a movie of my wedding and it plays perfectly until I export it. For some reason it then plays the audio from the end of the movie at the start!!
I can not figure out why.

I have a lot of free space on my start up disc ect - 25gb.
I have tried to re-create a new project and copy the details to the new project but the same thing happens.

I have run a disc utility repair.

It is really frustrating.

Can anyone please help??

Thank you 🙂