The causes of thin-film media noise are discussed by deriving a formula which shows a direct relationship between the noise spectrum and the magnetization configuration of a thin-film medium. This formula is derived by Fourier-transforming the autocorrelation function of jM(x)-M(z) along the track direction, where M(x) and M(z) are the longitudinal and vertical components of magnetization, respectively. Noise and signal spectra are computed by means of this formula. The computed noise spectra are the maximum for a relatively long wavelength. Their form and intensity are shown to be strongly affected by the anisotropy constant and the axis orientation of easy magnetization.