Spin-dependent changes in the noise power of undoped amorphous hydrogenated silicon ( a-Si:H) are observed under electron spin resonance conditions. The noise-detected magnetic resonance (NDMR) signal has the g value of holes in the valence band tail of a-Si:H. Both the sign of the NDMR signal and the frequency dependence of its intensity can be quantitatively accounted for by a resonant reduction of the generation-recombination noise time constant tau. This identifies hopping in the valence-band tail as the dominant spin-dependent step governing noise in this material.