Sustainable, biodegradable elastomers are needed to replace fossil-based alternatives and reduce the environmental impact of traditional vibration damping materials. We investigate agarose-based hydrogels as eco-friendly vibration absorbers, examining the combined effects of polymer concentration (1-7 wt%), relative humidity (55-98%), and mechanical pre-stress on their dynamic mechanical properties. Frequency-dependent viscoelastic and vibration transmissibility tests, supported by Gaussian process regression (GPR), reveal that increasing agarose concentration enhances the storage modulus (') by over an order of magnitude, reaching ∼5 MPa depending on humidity and applied prestress. Remarkably, the damping efficiency-characterised by the loss factor (tan())-exhibits a highly non-monotonic trend. Maximum energy dissipation is observed at intermediate network densities, with tan() up to 0.21 and a loss modulus of ∼515 kPa at 5 wt% and 75% relative humidity, comparable to synthetic elastomers and other advanced hydrogel composites. GPR analysis shows that prestress controls nonlinear stiffening and transmissibility resonance behavior, while shifting peak damping from 5 wt% to 1 wt% agarose as prestress increases. These findings underscore the mechanical tunability and sustainability of agarose hydrogels, providing potential design guidance for biodegradable vibration mitigation materials.