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

background_noise_function.rb

require "chunky_png"
require "base64"

module Sass::Script::Functions
  def background_noise(kwargs = {})
    opts = {}
    Sass::Util.map_hash({
        "intensity"  => [0..1,          "",   :Number, Sass::Script::Number.new(0.5) ],
        "opacity"    => [0..1,          "",   :Number, Sass::Script::Number.new(0.08)],
        "size"       => [1..512,        "px", :Number, Sass::Script::Number.new(200) ],
        "monochrome" => [[true, false], "",   :Bool,   Sass::Script::Bool.new(false) ]
      }) do |name, (range, units, type, default)|
      
      if val = kwargs.delete(name)
        assert_type val, type, name
        if range && !range.include?(val.value)
          raise ArgumentError.new("$#{name}: Amount #{val} must be between #{range.first}#{units} and #{range.last}#{units}")
        end
      else
        val = default
      end
      opts[name] = val
    end
    
    image = ChunkyPNG::Image.new(opts["size"].to_i, opts["size"].to_i)
    
    for i in (0..(opts["intensity"].to_s.to_f * (opts["size"].to_i**2)))
       x = rand(opts["size"].to_i)
       y = rand(opts["size"].to_i)
       r = rand(255)
       a = rand(255 * opts["opacity"].to_s.to_f)
       color = opts["monochrome"] ? ChunkyPNG::Color.rgba(r, r, r, a) : ChunkyPNG::Color.rgba(r, rand(255), rand(255), a)
       image.set_pixel(x, y, color)
    end
    
    data = Base64.encode64(image.to_blob).gsub("\n", "")
    Sass::Script::String.new("url('data:image/png;base64,#{data}')")
  end
  declare :noise, [], :var_kwargs => true
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(
  $intensity: $bg-noise-intensity-default,
  $opacity:   $bg-noise-opacity-default,
  $size:      $bg-noise-size-default,
  $mono:      false
) {
  background-color:   $color;
  background-image:   background_noise($intensity, $opacity, $size, $mono);
  background-repeat:  repeat;
}

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

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