When previewing, as the camera moves, the noise of the characters will be very serious, how can I solve this problem?
Your computer is not good enough to display a smooth preview video in the work window? Then there are three possible work-arounds:
1. Render the video and use the render window as a preview window.
2. Reduce the video resolution of your MMD project, enough to see a smooth preview video in the work window. Then restore the higher video resolution just before you render.
3. Purchase a better computer.