I have noticed that my Sony wm-40 will seems to pulsate (the note fades in and out) the sound on the notes AA and AAA (the two lowest AA's on the piano. I think its around 60hz). I'm not sure if I got a bad sub or if I managed to blow it out I was hoping that someone would have some suggestion on what to do about it. I tried other speakers on the same track and I didn't get the pulsating. Any help would be appreciated.