External fluctuation torques acting on gear trains having clearances often cause vibro-impact motions with resultant rattle noise issues. In this study, an impact-velocity based rattle severity parameter that correlates to the resultant rattling noise is proposed for multi mesh gear trains. An experimental setup is employed to measure torsional vibro-impact motions and the corresponding sound pressure levels of a a three-axis gear train under various torque fluctuation conditions. A discrete torsional model of the experimental setup is developed and validated through comparisons to the vibration measurements. An impact velocity-based rattle severity index defined from the predicted response is proposed and shown to correlate well with the measured rattle noise sound pressure levels within a wide range of operating conditions. The demonstrated ability of the proposed rattle severity index in tracking rattle noise allows for the assessment of rattle consequences of a multi-mesh drivetrain solely from its predicted torsional response.