This study presents an experimental and numerical investigation into the vibrational response of 3D-printed sandwich beams with three distinct core topologies: triangular, honeycomb, and a hybrid configuration combining both. The primary objective is to assess the influence of core topology on natural frequencies and modal damping ratios as key dynamic performance indicators. Specimens were fabricated using Fused Deposition Modeling (FDM) with Polylactic Acid (PLA) material, and impact hammer modal testing was conducted to extract the Frequency Response Functions (FRFs). Natural frequencies and damping ratios were subsequently derived using frequency-domain curve-fitting algorithms. For numerical simulations, a finite element model was developed in Abaqus and validated against the experimental data, yielding a relative error of less than 5%. The findings reveal that the hybrid core, despite having a nearly identical weight, consistently delivers the highest natural frequencies across all bending modes. Modal damping analysis indicates that while the honeycomb core exhibits superior energy dissipation behavior in the first mode, the hybrid core demonstrates a remarkable surge in damping at higher modes (fourth and fifth), which is attributed to the synergistic energy loss effects at the interface between the dissimilar topologies. The outcomes of this research confirm that the application of hybrid cores constitutes an efficient strategy for frequency spectrum engineering and damping control in lightweight sandwich structures.