Motorola KRZR K1m

I downloaded a podcast as an MP3 file in my hard drive and I made a copy of it on the memory card in "my sounds" folder. For some reason the phone doesn't see this file. I repeated the same with an other podcast, also an MP3 file. Again, the phone will show me the folder as empty. I put MP3 songs in "my music" and MP4 videos in "my videos" and I had no problem listening to or watching them. Any secret here? Thanks for your help