This study reports the results of an investigation on the break-up of viscous jets submitted to multimode piezoelectric stimulations. This is performed by modulating the exit velocity with non-sinusoidal perturbations. Previous experiments carried out with this type of stimulation have been limited in finding acceptable configurations for breakup essentially with the help of stroboscopic photographs of the jet behaviour. The spatial information obtained from analyses of photographs proves to be only sufficient to give tendencies. Temporal information is required to study the correlations between the satellite formation and the excitation imposed on the jet, and as demonstrated in this paper may be useful for testing theoretical models. In this work, we perform non-sinusoidal piezoelectric excitation experiments for various values of voltages and phase angle under stable and unstable conditions. The cases studied also include in-phase and out of phase superimposition of fundamental and overtones. Spectral analysis used in conjunction with a laser photometric method unveils the interactions between the fundamental and the harmonic components which grow at different rates and determine the final behaviour of the jet. In particular, we show how the non-linear interaction between the fundamental and the harmonics may be ascribed to the formation of a variety of dropsizes and shapes.