We have measured 1/f noise of single-grain-boundary junctions in superconducting Y1Ba2Cu3O7- epitaxial films. The origin of 1/f noise is identified and the data are used to rule out recent suggestions for new mechanisms which generate 1/f noise. Using ozone annealing, both 1/f noise and critical current density of the grain boundary were found to improve. However, the persistence of both noise and Josephson coupling suggest that oxygen deficiency at the boundary is not the sole cause of the anomalous coupling in these materials. We speculate that the depression of the order parameter is connected with the cores of the dislocations forming an array. © 1992 The American Physical Society.