The study of dynamical properties of crvstals near structural phase transitions is still of great importauce. Especially the interest on ultralow-frequency dynamics, i.e. the so called ‘Central-Peak question’ was renewed nowadays through some recent work on the observation of Entropy Fluctuations in macroscopic susceptibilities. This so called Heat-Diffusion Central Peak was previously found in scattering experiments, and the corresponding theory was originally formulated for scattering experiments. In this work we present an overview on previous light scattering measurements of Entropy Fluctuations and very recent results concerning the observation of a Heat-Diffusion Central Peak in macroscopic propertieslat ultralorv frequencies, which provide a new insight into the ‘old’ Central Peak problem. The crossover functions from isothermal to adiabatic behaviour are calculated for the macroscopic susceptibilities.