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 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 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 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 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. <EOS>