A formalism based upon the source-sink method of Horning, Feinberg, and Galanin has been developed which predicts the neutron noise spectrum, and time-dependent correlation function, in heterogeneous reactor systems. The method is applied to two problems in infinite plane geometry: the infinite lattice, and detector perturbations. In the lattice problem, it is shown that the simple, homogeneous theory will only be valid when the lattice spacing is very much less than the attenuation length of a neutron wave in the pure moderator. The flux depression in the neighborhood of a neutron detector is found to introduce significant corrections to the noise spectrum.