We present a detailed X-ray scattering study of the static and dynamic behavior of a styrene-isoprene diblock copolymer melt with a styrene volume fraction of 0.3468. At 115 and 120 degrees C, we observe splitting of the principal Bragg peak, which we attribute to phase coexistence of hexagonal cylindrical and cubic double-gyroid structure. In the disordered phase, above 130 degrees C, we have characterized the dynamics of composition fluctuations via X-ray Photon correlation spectroscopy. Near the peak of the static structure factor, these fluctuations show stretched-exponential relaxations, characterized by a stretching exponent of about 0.36 for a range of temperatures immediately above the MST. The corresponding characteristic relaxation times vary exponentially with temperature, changing by a factor of 2 for each 2 degrees C change in temperature. At low wavevectors, the measured relaxations are diffusive with relaxation times that change by a factor of 2 for each 8 degrees C change in temperature.