  I present the Floquet scattering matrix theory of low-frequency heat
fluctuations in driven multi-terminal quantum-coherent conductors in the linear
response regime and beyond. The intrinsic fluctuations of energy of dynamically
excited electrons are identified as the fundamental source of a heat noise not
revealed by the electrical noise. The role of backscattering in the increase of
a heat noise above the level defined by the Callen-Welton
fluctuation-dissipation theorem, is highlighted.
