Temporal variability of additional frequencies in RRab, RRd, and RRc stars. Upper left: lower panel: amplitude variation of the additional f′ = 2.61219586 d^-1 frequency of CoRoT Blazhko RR Lyrae star 434. The fundamental mode frequency, its harmonics, and the side peaks related to the modulation (and the modulation frequency itself) were removed. Upper panels: the vicinity of f′ in the frequency spectrum, lower panels: amplitude variation. Upper right: the same for the temporal variability of f′ = 4.4786159 d^-1 CoRoT RRd star 812. The first overtone frequency and its harmonics were removed. Lower left: temporal variation of the f′ = 4.37783 d^-1 frequency of CoRoT RRc star 241. The first overtone frequency and its harmonics were removed. Lower right: the same as for the RRc star 241, but for 652. The amplitudes are smaller than in 241, but the variation in the structure of the f′ = 5.82484 d^-1 peak is strikingly similar.