Methods, apparatus, systems and articles of manufacture are disclosed to reduce noise from harmonic noise sources. Example methods disclosed herein include determining a first point representing a comparatively large amplitude for a frequency value in an audio sample. Disclosed example methods also include generating a first contour trace of points having amplitude, frequency and phase values within thresholds from the first point of comparatively large amplitude. Example methods include generating a second contour trace of points having amplitude, frequency and phase values within thresholds of a second point of comparatively large amplitude. Disclosed example methods include calculating a parameter for each of the contour traces and determining if the first or second contour traces represent outliers based on the parameters. Disclosed example methods also include, in response to determining the contour to be an outlier contour trace, removing the outlier contour trace from the audio sample.