Static and dynamic low-angle light-scattering experiments carried out on semidilute and moderately concentrated solutions of polystyrene in toluene provide evidence for the existence of heterogeneities in the entanglement network with correlation lengths of several hundred nanometers. The slow mode showing up in the correlograms in addition to the gel mode reflects the diffusive motion of these chain associations. The tendency to form associations increases with the solute concentration and with decreasing temperature. The observations indicate that the reptation time does not represent the longest relaxation time in the system; a complete reorganization of the entanglement network requires a much longer period.