1. A system for monitoring and indicating acoustically the operating conditions of a motor vehicle, comprising: a plurality of sensor devices, each arranged to monitor a respective physical or operating magnitude of apparatus, a device or a member of the vehicle, and to provide corresponding electrical signals, acoustic signal generator means for generating a plurality of acoustic characterising signals, each indicative of a corresponding predetermined operating condition of a predetermined plurality of operating conditions, and a plurality of acoustic level signals indicative of corresponding predetermined levels of importance or seriousness attributable to the operating conditions, and processing means connected to the sensor devices and the acoustic signal generator means and arranged: to detect on the basis of signals provided by the sensor devices the occurrence of the operating conditions of the vehicle, to attach in a predetermined manner a predetermined level of seriousness or importance to each operating condition, and to supply to the acoustic signal generator means electrical control signals for causing the output of an acoustic signal comprising, in succession, the acoustic level signal and the acoustic characterising signal associated with the operating condition detected at any time.