Using 3D noise to create simple animated texture. Here, the third dimension ('z') is treated as time. 

increment = 0.01
# The noise function's 3rd argument, a variable that increments
# once per cycle
zoff = 0.0
# We will increment zoff differently than xoff and yoff
zincrement = 0.02


def setup():
    size(640, 360)
    frameRate(30)


def draw():
    global zoff
    # Optional: adjust noise detail here
    # noiseDetail(8,0.65f)
    loadPixels()
    xoff = 0.0  # Start xoff at 0

    # For every x,y coordinate in a 2D space, calculate a noise value and
    # produce a brightness value
    for x in range(width):
        xoff += increment     # Increment xoff
        yoff = 0.0     # For every xoff, start yoff at 0
        for y in range(height):
            yoff += increment  # Increment yoff

            # Calculate noise and scale by 255
            bright = noise(xoff, yoff, zoff) * 255
            # Try using this line instead
            # float bright = random(0,255)

            # Set each pixel onscreen to a grayscale value
            pixels[x + y * width] = color(bright, bright, bright)
    updatePixels()
    zoff += zincrement  # Increment zoff