Thanks for the tip. It does not use FX lists for the existing sound. Rather from what i can see in Game.dat using a hex editor, i think the module is hard coded to use the HijackDriver voice in voice.ini.
Rather than bloat my mod by including voice.ini in it just to modify one sound, i fixed it by adding HijackDriver to Weapon.ini which is in my mod. Since the word "Weapon.ini" is alphanumerically later in order than "voice.ini", the game will use the HijackDriver sound specification in weapon.ini instead of the one in voice.ini.
Here is what i put in weapon.ini:
Sounds = ;
Attack = ;
Control = random
Volume = 0
MinVolume = 0
Type = world shrouded everyone