As airflow and power output is increased, the majority of Mk3 Focus RS exhibit a high-pitched whistling noise - most noticeable on cold start and with light throttle applications. 

The ZERONINE Design volume reduction chamber replaces the OE turbo resonator and has been engineered to suppress the acoustic frequencies being generated across the turbocharger compressor housing - think of it like noise cancelling headphones for your turbocharger.

Despite its simple appearance, the VRC's dimensions, the materials used and internal configuration all play a crucial role in cancelling out this unwanted NVH (Noise / Vibration / Harshness).