Glitched audio playback when using the [Sound] section

I'm using [Sound] with multiple files, and all of them seem to glitch out before the volume completely goes away, as demonstrated in this video:

Basically, the volumefunction is designed so that certain sounds only play at certain speeds of the train.
Here's the code to one of the motor files:

Code:

[object]
States = ExceptionCode.b3d
TrackFollowerFunction = speed * 2.23694

[sound]
Filename = motor1.wav
Volumefunction = if[value + 1 * (speed * 2.23693629) >= 3.5 & value + 1 * (speed * 2.23693629) <= 6.7,if[powerNotch > 0,1,0],0]
Pitch = 1.0
Position = 0,1.2,0
Radius = 100