my method is to make a .jpg in photoshop. Load in any picture, that is slightly larger than your flash stage dimensions. Apply a filter called 'Add Noise'. Turn the amount up to 400%. Voilá! Static .jpg. How you use it in Flash depends what you're going to do with it. You could put 4 frames of it into a movieClip and rotate each frame 90 degrees, and add a gotoAndPlay(1) action on the last frame of the movieClip timeine. Or, you could script the whole thing with some code like:
on(enterFrame){
this._rotation += 90;
}
The choice is yours. Hope this helped :D