Results from a joint DARPA/Boeing/NASA/Army wind tunnel test demonstrated the ability to reduce in-plane, low-frequency noise of the full-scale Boeing-SMART (Smart Material Actuated Rotor Technology) rotor with active flaps. Test data reported in this paper illustrated that near-field acoustic energy in the first six blade-passing harmonics could be reduced by up to 6 dB at a moderate-airspeed, level flight condition at an advance ratio of 0.30. Reduced noise levels were attributed to selective active flap schedules that modified in-plane blade airloads on the advancing side of the rotor, generating counteracting acoustic pulses that partially offset the negative pressure peaks associated with in-plane, steady thickness noise. These favorable reduced-noise operating states are a strong function of the active flap actuation amplitude, frequency, and phase. The reduced noise levels resulted in reduction of predicted aural detection distance, but incurred vibratory load penalties due to increased hub shear forces.