So you want it silent then have the sound and have the sand soung put on?
Maybe its cause any sound put on when volume is 0, stays silent and will only work if volume is above 0. Something like that may be the reason, but I dunno.
I was going to question the calling of a script, but that's prolly what calls for the sound. duh...
I'd have to go with my suggestion above even though I just thought of it and it could be totally wrong. Why not toy with sound levels of 0.1 or something like that?