Method of optimizing the noise generated by a rotorcraft on the ground, said rotorcraft comprising: - a hybrid power plant provided with at least one fuel-burning engine and at least one electric machine; - at least one rotor (2,3) rotated by said hybrid power plant and - at least one electrical power source powering said at least one electric machine with electricity by means of an electrical network; characterized in that said method comprises the following steps: - first check that said rotorcraft is on the ground by a detection device, - second check by a control unit of whether said at least one fuel-burning engine is in the started state or stopped state, and its speed; - third check by a control device of whether said at least one electric machine is in the started state or stopped state, and its speed; - first control step by means of said control unit of at least one fuel-burning engine among said at least one fuel-burning engine, of which said state is started if said rotorcraft is on the ground, in such a manner as to control a speed of said at least one fuel-burning engine until said at least one fuel-burning engine reaches a predetermined speed referred to as the "silent speed", said silent speed being a slower speed of said fuel-burning engine allowing the noise generated by said fuel-burning engine to be reduced, - second control step by means of said control device of at least one electric machine, such that said at least one electric machine delivers mechanical power to drive said at least one rotor (2, 3) and - determination by an anemometer of a speed of the wind around said rotorcraft and of whether said speed of said wind is greater than a predetermined limit, said second control step of at least one electric machine is not performed or else is stopped. - a hybrid power plant provided with at least one fuel-burning engine and at least one electric machine; - at least one rotor (2,3) rotated by said hybrid power plant and - at least one electrical power source powering said at least one electric machine with electricity by means of an electrical network; - first check that said rotorcraft is on the ground by a detection device, - second check by a control unit of whether said at least one fuel-burning engine is in the started state or stopped state, and its speed; - third check by a control device of whether said at least one electric machine is in the started state or stopped state, and its speed; - first control step by means of said control unit of at least one fuel-burning engine among said at least one fuel-burning engine, of which said state is started if said rotorcraft is on the ground, in such a manner as to control a speed of said at least one fuel-burning engine until said at least one fuel-burning engine reaches a predetermined speed referred to as the "silent speed", said silent speed being a slower speed of said fuel-burning engine allowing the noise generated by said fuel-burning engine to be reduced, - second control step by means of said control device of at least one electric machine, such that said at least one electric machine delivers mechanical power to drive said at least one rotor (2, 3) and - determination by an anemometer of a speed of the wind around said rotorcraft and of whether said speed of said wind is greater than a predetermined limit, said second control step of at least one electric machine is not performed or else is stopped.