**Summary:** This paper presents a rigorous mathematical analysis of subwavelength resonant acoustic scattering in fast time-modulated media. The study focuses on a high-contrast resonator with a time-modulated density, where the modulation frequency is much larger than the incident wave frequency. The analysis shows that the fast time modulation averages out over time, and the system behaves like an unmodulated resonator with an effective density. However, under specific tuning of the modulation, temporal Sturm-Liouville eigenvalues align with spatial Neumann eigenvalues, enabling low-frequency incident waves to excite high-frequency modes in the resonator. This leads to the generation of high-frequency components in the far field and exponentially growing outgoing modes. The study identifies that such systems could serve as spontaneous radiation sources or high-harmonic generators. The analysis involves a Dirichlet-to-Neumann approach, modal decomposition, and effective medium theory. Key findings include the derivation of subwavelength resonant frequencies and the existence of exponentially growing modes under exceptional modulation conditions. The work provides a mathematical framework for understanding wave scattering in time-modulated media, with potential applications in acoustic metamaterials and wave manipulation.**Summary:** This paper presents a rigorous mathematical analysis of subwavelength resonant acoustic scattering in fast time-modulated media. The study focuses on a high-contrast resonator with a time-modulated density, where the modulation frequency is much larger than the incident wave frequency. The analysis shows that the fast time modulation averages out over time, and the system behaves like an unmodulated resonator with an effective density. However, under specific tuning of the modulation, temporal Sturm-Liouville eigenvalues align with spatial Neumann eigenvalues, enabling low-frequency incident waves to excite high-frequency modes in the resonator. This leads to the generation of high-frequency components in the far field and exponentially growing outgoing modes. The study identifies that such systems could serve as spontaneous radiation sources or high-harmonic generators. The analysis involves a Dirichlet-to-Neumann approach, modal decomposition, and effective medium theory. Key findings include the derivation of subwavelength resonant frequencies and the existence of exponentially growing modes under exceptional modulation conditions. The work provides a mathematical framework for understanding wave scattering in time-modulated media, with potential applications in acoustic metamaterials and wave manipulation.