Are you using iTunes? If you are using iTunes & have it set to copy songs across, it will 'copy' them into its own music library. So will end up with a copy in your download folder & another in your iTunes music folder.

However with you suggesting up to 8 copies, that does sound odd. Can you check their location? Incomplete files may show up in the library.
Right-click the file in library, choose get file information .. this info window will show their location.