There are 3 places weapon sounds can be set and they have an order of precidence:
The .ini sets the "Default" sound this can be overridden by the weapon's sound field in the relevant unit (in the units tab mobhack), which in turn can be overidden by the weapon sound (sound field in the weapon tab in mobhack). If any field has a 0 in it then it defaults to the next lower level - ie wpn>unit>default.
Hope this helps track down your wayward sounds
See
THIS thread