The fresh, clean ice that dominates Enceladus' surface makes it the most reflective surface of any Solar System body across a broad range of wavelengths, from visible to microwave. Fine-grained micron to tens of micron particles resulting from plume or E-ring deposition dominate optical wavelengths, enabling enhanced geometric albedo due to coherent backscatter. However, high albedo at centimetric radar wavelengths suggests scattering from characteristic spatial scales of millimetric or greater. To date, no single model of surface material structure has been proposed that can explain all the observed phenomena. We propose that sintering of fine particles during past periods of low or zero cryovolcanic activity may create subsurface layers that enhance radar backscatter sufficiently to explain the observations. The thickness of the upper, unsintered layer is likely at least 1-2 cm, and probably well under a meter. More modeling and laboratory work is required to test the validity of our assertion that sintering during quiescent periods of plume activity is responsible for the enhanced radar backscatter.