Music out of sync after rendering

Hi.

I created a little video using clips I found on the Internet, and added a music piece to the project. When I watch the project, everything looks perfect, but when I save it as a film, music is out of sync (it's less than a second, however, it is important that a rain drop falls together with a piano sound). I have tried saving it many times, but nothing seems to work. Could anyone please help?