It is widely known that the gear fault signal is affected by the interference of strong background noise and the loss of internal fault excitation transmission, which weakens the features of incipient fault signals and makes gear fault diagnosis difficult. Motivated by the acoustic manipulation capabilities of acoustic metamaterials and the gear modulation principle, this study proposes a front-end perception method for weak gear fault feature diagnosis via gradient acoustic metamaterials (GAM), which utilizes the acoustic rainbow capture and compression ability to reduce the difficulty of gear incipient fault diagnosis. Considering the FM/AM modulation principle, acoustically enhanced sensing for fault features can be achieved by collecting components from the selected air gaps in the GAM structure. The feasibility of GAM-based gear weak fault feature diagnosis is proved by experiments, which illustrate the multiscale feature denoising and frequency-selective enhancement characteristics of GAM. The results show that the amplitude of the target signal is amplified by more than eight times, the sideband component containing the fault signal is clearly enhanced, and the effect of denoising outside the target sideband is evident. This allows the weak fault features to be easily identified. Compared to digital filtering in traditional post-processing methods, the proposed approach is more straightforward for extracting weak fault features. Additionally, this method adopts a non-contact measurement method with the MEMS microphone for front-end enhancement and sensing. Finally, it can be seen that the proposed method has great potential for structurally enhancing the perception of gearbox weak fault signal denoising and feature diagnosis.