The first thing you should consider is if the noise can be eliminated altogether. You could:

• Try using quieter equipment or processes – consider noise levels when purchasing equipment, replace the noise
• Have controls: avoid metal on metal contact, add material to reduce vibration noise, try to isolate noise and fit silencers to air exhausts.
• Try to lessen the noise that the surrounding people encounter – set up enclosures around machines and block direct sound with barriers
• Create a workplace from the beginning to try and lessen noise – materials that absorb noise, design the workplace to keep machinery out of high people trafficked areas