I know nothing about stone crushers (I suspect there is a limited knowledge base here about the subject generally). I do know a little about acoustics though.
I suspect that crushing stone is inherently a noisy activity, so what you probably have to do is:
1)To look at how that noise is contained.
2) Ensure that the equipment used is not amplifying the noise that is made.
The first usually has some effect on the second.
Some years ago, "sound deadening" kits were available for cars. These were felt/cloth components that would be attached around the engine bay which had the effect of "keeping the sound in" but almost as importantly, stopping the metal panels vibrating and thereby amplifying the sound. ("Drumming").
People who bought such kits were often surprised to find components for fitting inside the boot lid and doors, just to prevent drumming.
So - the courses of action are, sound insulation and amplification prevention.