If it's the window at left, then it is blurred reflections rendered at too low quality setting. If it's the material close to it, then it's a material issue (a noisy material). In fact, I can see the same amount of noise on all parts of it (lit parts and shaded parts). The shadows themselves appear to be ok from what i can see (e.g.on the grey car) Try replacing the grainy material that surrounds the windows with a smooth material and see if the problem persists, in which case post another picture.