Photon correlation spectroscopy has been used to investigate the dynamics of composition fluctuations in disordered semidilute solutions of (polyisoprene)(2)(polystyrene) (I2S) graft copolymers in toluene. Four different relaxation mechanisms were identified with different concentration and wavevector dependencies: Three are the well-known processes in diblock copolymer solutions (cooperative diffusion, internal mode, and polydispersity diffusive mode), whereas the fourth is an extra process between the internal and the polydispersity modes that appears near the disorder-to-order transition. The latter displays similar characteristics to a process recently observed for inverse starblock copolymers also in the ordering region, and should be related to the macromolecular architecture.