The sound from two 5600 HP induced draft fans at a 500-MW coal-fired power plant was a source of community annoyance. Each fan was retrofitted with a V-notch cutoff designed to reduce the noise generated at the blade passage frequency and its harmonics. The cutoff is the part of the fan casing at the discharge which is closest to the impeller blade tips. A conventional cutoff has a straight edge parallel to the blade tips, while the edges of a V-notch are askew to the blade tips. The V-notch design was based on aerodynamic tests of a 116 scale model fan with inlet and discharge ducts. In order to evaluate the performance of the V-notch cutoff, detailed sound measurements were taken in the community, near the fan cases and inside the stack (in 330°F hot flue gas) both before and after the fan modifications. In addition, the in-stack measurements were coincident with fan performance measurements and were taken for several operating conditions. A 5- to 7-dB reduction of the tones was achieved which significantly reduced complaints.