Despite extensive research on nudging techniques aimed at promoting green consumption, the influence of natural sounds on encouraging environmentally friendly behavior remains relatively understudied. It is valuable to examine how sounds matter in green marketing, as more and more firms are using background sounds in video advertisements. Drawing on the Stimulus-Organism-Response model, we propose that natural sound increase early attentional congruency associated with green products, thereby promoting customers' purchase of green products. To test on our theory, we conducted an experiment using an event-related potentials (ERP) method and employed a hierarchical drift-diffusion model (HDDM). The results show that compared with unnatural sounds, natural sounds not only increased the purchase rates for green products but also enhanced decision-making efficiency (drift rate) in favor of purchasing green products. Additionally, consumers also exhibited a reduced frontal early P2 wave (150-230ms) in response to green products under natural sounds, indicating that natural sounds increased the early attentional congruency associated with green products. More importantly, the early attentional congruency provides an explanation for how natural sounds nudge the efficiency of purchasing decisions for green products. This study thus contributes to the discovery of a new psychological path that helps deepen our understanding of how natural sounds can nudge green consumption. It also provides actionable implications for green consumption market managers.