When hitting a bar several higher frequency, shorter wavelength oscillations are created among its oscillations. On the standing-waves formed here it can be seen even better that the oscillation nodes do not follow one another at regular intervals, so we do not get smooth regular lines. These higher frequency oscillations are not harmonics of the fundamental frequency oscillation.
E.g.: f₁=6,27f₀ and f₂=17,57f₀.