Are you PAL?
I use NTSC. Perhaps it's a problem when I created the song I can give a brief writing on what I did.
I downloaded all tools and placed them in C:/brawlmusic (no spaces). I then ran gwave and opened a mp3 file song. I saved the song in my brawlmusic folder as a .wav 16bit stereo. I didn't edit the song at all because I didn't think it needed it. I then right clicked the left speaker(green), pressed channel, and then saved selection as "loftyL". I did the same for the right speaker and called it "loftyR". I then ran Start.bat, selected B, typed in w23, and then deleted w23R & w23L. I renamed both loftyR to w23R and loftyL to w23L. I then continued with Start.bat and waited. When it asked me to input the starting point I typed 0 and continued. I named my brstm file lofty. I opened my EditedSongs folder and renamed it to X03. I then stuck it into my SD card under strm.
Not sure if this will help, but I'm thinking it may be because of the rename, I'll test it out.