1. Start with a blank image.
  2. Use the Add Noise filter to add around 80% monochromatic uniform noise.
  3. Now apply a horizontal Motion Blur of about 100 pixels.
  4. Under the Other filter category, choose Offset.
  5. Choose a horizontal offset of around 150 pixels and select Wrap Around.
  6. Now use the rubber stamp tool (with a largish brush) to erase the seam.

Pretty seemple, eh?