Audio problems in iMovie11 after exporting

Hey everyone!

I have been suffering from a problem that I have no clue how to fix. So I created my video 9min long with all sorts of stuff (logos, various songs, voicerovers, detached audio, attached audio haha, cutaway picture, etc etc) and everything is fine with the sound while its still in the library. The movie is made and ready to export. BUT when I export and create a .mov file (HD 780 or 1080) the sound gets messed up and sudden gaps of silence appear out of nowhere. Usually those gaps appear at the end of the clip. Also the more I export the movie the more problems it appears to have..... So now besides the silence gaps, in 2 scenes the sound goes like you're under water for a second or so, and then goes back to normal. AGAIN this happens ONLY after exporting. Before rendering everything is fine on my imovie, sound is in tact and whatnot. But after exporting I face these issues that I have to solve somehow..

Please help someone, it's urgent!

Thank you in advance.