I believe Unity, and therefore Ravenfield, has a maximum amount of audio clips it can play at once (256?) - I'm not sure if there's a workaround for this.

if by that you mean listen to the sound files, im pretty sure all of them are included in the rftools pack. but unfortunately as creepa said only so much audio can play at once which can lead to jets making you jump as their sound cuts in or out of nowhere xd