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SPIDER is the full scale prototype for the ITER Heating Neutral Beam source, hosted at the Neutral Beam Test Facility in Padova, Italy. The behavior of the beam must be thoroughly investigated to bring the machine's performance in line with ITER's requirements. In particular, ripples in the beam can affect its divergence. Measuring the AC component of the beam current can therefore help to understand the impact that the oscillations caused by the source power supplies or RF generators have on the beam optics. To minimize the occurrence of electrical discharges, SPIDER was recently operated with a mask designed to close a large number of extraction apertures. As a consequence, the space between each beamlet was substantially increased, allowing for the installation of the Beamlet Current Monitor (BCM) which enables a non-invasive direct measurement of the DC and AC components of the currents of 5 individual beamlets. A first assessment of the beamlet currents' AC components (up to 10 MHz) was performed during SPIDER's first campaign with cesium evaporation. Recurring oscillations were identified in various frequency ranges, with amplitudes reaching up to ∼ 7% of the beamlet current DC value. When possible, the ripples were correlated to oscillations due to the RF oscillators and the beatings caused by their mutual coupling, or to SPIDER's power supply systems. • The AC component of the ion beam in SPIDER was characterized with the BCM diagnostic. • The beam features ripples due to the RF oscillators and their beatings. • Power supply oscillations at multiples of 50 Hz are seen in the plasma and the beam. • A 138.8 kHz ripple caused by the EG power supply can reach very large amplitudes. [ABSTRACT FROM AUTHOR]