Bayesian generalized Lomb–Scargle periodograms for various subsets of the published CARMENES and HARPS RVs with one of a pair of possible weighting schemes. The details of the time-series shown in each panel are annotated above the panel. The three dashed vertical lines depict the orbital period of the proposed non-transiting planet K2-18c (P_c = 8.962 days), the orbital period of the known transiting planet K2-18b (P_b = 32.93963 days), and the photometric stellar rotation period (P_rot = 38.6 days). The P_c signal posited to be due to a second, non-transiting planet is seen at high relative probability in all but the full CARMENES RV time-series from S18 with a weighting.