Although inherent to turbomachinery, unsteady operation reduces performance, reliability and acoustic comfort in centrifugal pump installations. Given the widespread use of these systems, the mechanisms driving such unsteadiness have been extensively investigated. Among them, the impeller-volute interaction has been recognized as the dominant source. In contrast, the role of cavitation is less frequently addressed even though it is responsible for a significant share of pump failure events. This knowledge gap is mainly due to the challenges encompassed by the analysis of cavitating flows, with the numerical tools for its modelling still being under active development. In this work, the new unsteadiness mechanisms introduced by cavitation and their influence on pump dynamics are examined. For this purpose, a numerical URANS dataset built applying the cavitation model developed by the authors is employed. Calculations are conducted at three different working points –50%, 100% and 160% of the nominal flow rate– each evaluated at four cavitation numbers, ranging from inception to performance breakdown. The flow field at the impeller-volute interface is decomposed in the frequency domain, allowing to decouple cavity-induced and impeller-volute fluctuations. This approach provides theoretical insight into the onset of cavitation-borne unsteadiness, marking the transition to a cavity-governed dynamic regime when the cavitation number is reduced. Furthermore, the effect of cavitation on pressure fluctuations is quantified: oscillation amplitudes up to 10% of the pump head can be attributed to the new unsteadiness mechanisms introduced by cavitation on their own. These findings highlight previously unidentified effects and offer a foundation for their early mitigation during the design phase, ultimately contributing to improved efficiency and reliability of future pump designs.