An aircraft environmental conditioning system is disclosed having an air cycle machine for conditioning an airflow comprising hot compressed air by reducing its temperature and pressure. The air cycle machine is disposed in a housing in an unpressurized area of the aircraft, and produces conditioned pressurized air for delivery to a pressurized area of the aircraft. The system also includes a vibration sensor disposed within the housing, and a controller in communication with the vibration sensor that is configured to respond to vibration detected by the vibration sensor.