<p>Background noise limits signal extraction in biological neural systems and neuromorphic circuits, particularly when fluctuations are shared across channels. Here we study an opponent-channel differential readout formed by two parameter-matched Rulkov neurons driven by opposite-polarity inputs and common-mode noise. Across exponential-decay, alpha-function, step, and sinusoidal stimuli, the differential readout improves waveform preservation and reference-aligned signal retention relative to single-neuron and amplitude-matched controls, especially when the shared-noise component is substantial. Robustness tests further show that the advantage decreases under weak noise correlation or large parameter mismatch. Mechanistic analysis reveals that common-mode noise is not completely eliminated in the nonlinear map: it perturbs the common operating state and re-enters the differential channel through state-dependent gain and local slope mismatch. These results identify both the benefit and the nonlinear leakage limit of differential readout in paired Rulkov-neuron dynamics.</p>