A new mechanism of low frequency (1/f-like) noise generation is described and analyzed. It is attributed to higher frequency asymmetric resonance modes, which are stimulated by a random factor, e.g. due to thermal excitation. One-dimensional models of bi-harmonic and non-linear asymmetric oscillators are presented to prove the concept, and a method of detecting the effect is developed. The method is then applied to experimental data, in order to show that the effect exists in magnetoresistive readers.