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We report the results of the temporal and spectral analysis of the longest BeppoSAX pointing (about 770 ks) of the microquasar GRS 1915+105, performed in October 2000. For the largest fraction of the observation GRS 1915+105 was in the so called ρ-mode, characterized by series of sharp pulses with a typical recurrence time of about 50 s, well detectable in the energy range 2-10 keV. This quasi-periodic behaviour was generally quite stable but, occasionally, it changed to a more irregular state in which the pulses are broader and their recurrence time is highly fluctuating. We found that this irregular ρ-mode is associated with an enhanced emission at energies greater than 15 keV. Wavelet analysis of the (2–10 keV) light curves is used to study the time evolution of the ρ-mode. [Copyright &y& Elsevier]