File size way too big

Hi everyone... I'm hoping someone can enlighten me. I can't find this topic in the list so just wondering if it's a new issue.

The issue - 

I've created a 20 page course. The course has audio and video (seperate files) within some of the pages. The video files (5 of them total just under 600MB) and the Audio file (total approx 6MB)... However the file size of my document is growing. I'm pretty clued up with files sizes for Video/Audio/Images.... but for some reason the .story file size keeps growing!!

I have tried compressing the video and replacing the files, but when I do this the file size grows??? Is Storyline 3 referencing old versions of the files ON TOP of the new files... I'm baffled... the file size should be going down not up (now that I've replaced the videos with smaller filesized verisons).

Currently I've removed all video files for a test and at this point the .story file is now over One Gig! And I've no idea why!

Any help would be gratefully received

Thanks all!

D