I can produce scratchy sounds when I mess with the file extension: For instance, a wave file that has had its extension changed to .cdg, or maybe an mp3-g, which has the extension .cdg but is not appropriate for the program. If the file is not 20 to 50 or more magabytes big, it is probably an mp3-g and will not work properly. It sounds like you have a full complement of programs to create the right files. If what I said is something that helps you or someone else, then I am happy.
Hope you have resolved the problem.