The electric machine can "meet its design requirements and the transmission meet its design requirements, but the combined system fails due to subsystem interactions." That failure covers both comfort and mechanical issues: "Drivetrain noise is more exposed due to little or no engine noise; electric machine excitations (radial forces, torque ripple) and drivetrain excitations (transmission error); complex interactions between electric machine and drivetrain; and high speeds causing dynamic unbalance
Arvan, "Research on the cross-coupling of a two axes gimbal system with dynamic unbalance
," International Journal of Advanced Robotic Systems, vol.
Mechanically induced noise is generated by impacting metal parts, such as gear teeth clashing, vanes sticking in slots, pump misalignment, dynamic unbalance
, excessive wear in components, valve noise, vibrating tubing, resonance in the system, etc.