Observed differences between measured and calculated elastic constants for Ti3SiC2 are investigated using Density Functional Theory and Inelastic Neutron Scattering. The agreement between the calculated lattice dynamics and the dynamics measured by inelastic neutron scattering is considered good except at energies below similar to 20meV where discrepancies suggest anharmonic potentials. This suggestion is confirmed by Density Functional TheoryMolecular Dynamics simulation which shows multiple site occupancy of the Si atoms within the basal plane at finite temperature and produces a calculated inelastic spectrum in better agreement with the measured spectrum in the low-energy region. The highly anharmonic potential energy surface of the Si atoms offers an explanation for the failure of elastic constants, calculated based on the harmonic approximation, to agree with initial experimental measurements.