Sass implementation of the Noisy jquery plugin: https://github.com/DanielRapp/Noisy

background_noise_function.rb

require "rubygems"
require "chunky_png"
require "base64"

module Sass::Script::Functions
  
  def background_noise(c, noise = 0.5, opacity = 0.08, size = 200, mono = false)
    
    # Convert SASS numbers to Ruby classes
    noise   = noise.to_s.to_f   if noise.is_a? Sass::Script::Number
    opacity = opacity.to_s.to_f if opacity.is_a? Sass::Script::Number
    size    = size.to_i         if size.is_a? Sass::Script::Number
    mono    = mono.to_bool      if mono.is_a? Sass::Script::Bool
    
    # Create the background image
    bg_color = ChunkyPNG::Color.rgba(c.red, c.green, c.blue, (c.alpha * 255).round)
    bg_image = ChunkyPNG::Image.new(size, size, bg_color)
    
    # Create a transparent foreground image
    fg_image = ChunkyPNG::Image.new(size, size)
    
    # Add some noise to the foreground image
    for i in (0..(noise * (size**2)))
      x = rand(size.to_i)
      y = rand(size.to_i)
      r = rand(255)
      a = rand(255 * opacity)
      color = mono ? ChunkyPNG::Color.rgba(r, r, r, a) : ChunkyPNG::Color.rgba(r, rand(255), rand(255), a)
      fg_image.set_pixel(x, y, color)
    end
    
    # Mix it up
    image = bg_image.compose(fg_image)
    
    # Save the image - will eventually save to a file but for now
    # a base64 data url will do...
    data  = Base64.encode64(image.to_blob).gsub("\n", "")
    Sass::Script::String.new("url('data:image/png;base64,#{data}')")
    
  end
  
end

background_noise_mixin.scss

$bg-noise-intensity-default:  0.5;
$bg-noise-opacity-default:    0.08;
$bg-noise-size-default:       200;

@mixin bg-noise($color,
  $intensity: $bg-noise-intensity-default,
  $opacity:   $bg-noise-opacity-default,
  $size:      $bg-noise-size-default,
  $mono:      false
){
  background-color:   $color;
  background-image:   background_noise($color, $intensity, $opacity, $size, $mono);
  background-repeat:  repeat;
}

@mixin bg-noise-mono($color,
  $intensity: $bg-noise-intensity-default,
  $opacity:   $bg-noise-opacity-default,
  $size:      $bg-noise-size-default
){
  @include bg-noise($color, $intensity, $opacity, $size, true);
}

body {
  @include bg-noise(#cecece);
}

Awesome! I love it. Exactly the kind of noise I was hoping for. You should definition make a small gem out of this one...it will be super valuable.