mp4 turning into mp3

I always import a folder into premiere with the videos i'm about to edit. When I import the folder (with usually about 20-30 one minute videos) a third or sometimes half of the clips turn into mp3. I can fix this by just dragging the videos out of the folder and importing them again into the project, than its good. But it would be nice to just being able to start editing right away instead of dealing with this problem over and over again.