In the three-dimensional Dirac semimetal Cd3As2 we notice an interplay of electronic and phonon degrees of freedom mediated by topological effects. There exist a pronounced quasielastic scattering and an anomalous anharmonicity of optical phonons. These effects follow a similar temperature dependence with a characteristic temperature T* ~ 100 K. Furthermore, there exist a resonant enhancement of phonon scattering intensity as function of incident photon energy. This energy of 1.9 eV coincides with interband electronic transitions in Cd3As2. A refined analysis shows that these effects are coupled via interband transitions in the Dirac states in Cd3As2 and a degeneracy of phonon energies with thermally excited electronic states. This degeneracy enhances energy density fluctuations. ; Comment: 9 pages