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We present recent results from our γ-ray transition-edge sensor (TES) microcalorimeters. We have demonstrated an energy resolution of 52 eV at 60 keV with devices composed of a high-purity Sn absorber and a Mo/Cu multilayer thin-film TES. In this paper, we present a detailed noise analysis of these devices and show that the major noise sources are device originated (thermal fluctuation and Johnson noise). Our performance analysis explicitly includes the noise contribution due to the composite geometry of these devices and electro-thermal feedback (ETF).