The VOLUME =
parameter in the background sound tag sets the volume. A volume
of zero is set at maximum, as loud as the user has the volume
control set. To lower the volume, try experimenting in increments
of -100.
This is the
line in the script you would change, starting with VOLUME=-100.
Lower the
volume again by changing the value to -200, -300 and so on until
you are satisfied with the results.