Fuel Truck AI Sound

The loudness of the fuel truck has annoyed me for some time, and I find that no sound slider has any affect on the volume of it's engine sound. I checked it's soundai.cfg file and found that changing OutsideConeVolume has no affect on the engine sound volume. Therefore, the only sucess I've had in quieting the truck is to substitute the automobile wav files. Does anyone have another solution?I did a search on the forum and found nothing, except there may be a means of changing the volume in the wav files.