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• Within European project CORTEX on reactor noise analysis. • One out of four articles on the experiments for CORTEX. • Unique modulation experiments in two zero power experimental reactors. • Perturbations: vibrating absorber (AKR-2), fuel rod vibration (CROCUS), absorber of variable strength (both AKR-2 and CROCUS) • Focus on experiments design and setup, including feedback from experience (three campaigns per facility) and modelers/work package on validation. • Novel miniature neutron detectors developed and used (MiMi detectors), based on scintillation (ZnS(Ag):6Li), optical fibers, and SiPM technology. We present the experimental campaigns – namely, three per facility – carried out between 2018 and 2021 in the AKR–2 and CROCUS zero power reactors within the framework of the Horizon 2020 European project CORTEX. Their purpose was to produce high-quality and noise-specific experimental data for the validation of the neutron noise computational models developed in CORTEX. In both reactors, perturbations were induced by two devices, separately and altogether. In AKR–2, they consisted of a rotating absorber, i.e. an absorber of variable strength , and a linear oscillator, i.e. a vibrating absorber , both sets in horizontal channels close to the core. In CROCUS, the project benefited from the COLIBRI experimental program and its fuel rods oscillator set in the outer lattice; an additional vibrating absorber called POLLEN was set in a vertical air-channel at core center. The campaigns at both facilities consisted of neutron measurements with numerous detectors at reference static states, and with the addition of the mechanical perturbations to induce neutron reactivity modulation. The present article documents the experimental setups and measurements for each facility and perturbation type. A focus is set on the experimental designs and their evolution along the project, as well as motivations and learned lessons. Results are presented and discussed in details in associated papers. [ABSTRACT FROM AUTHOR]