I want to add video noise/grain based on an audio track?
You can convert audio to keyframes. Right-click the footage with the audio, and choose Animation>Keyframe Assistant>Convert Audio to Keyframes, or with the audio layer selected go to the Animation menu in the menu bar. 



This will create a new layer with keyframes for the intensity of the audio. You can copy those keyframes on to any property that you want to animate and adjust them in the graph editor, or you can use an expression on the property and select the keyframes with the expressions pickwhip. This means that the audio levels can control any animatable property including parameters for your favourite noise effect.

A useful trick is that you can apply EQ to the audio before you convert it to keyframes and have different sets of keyframes for the bassline and the melody sounds.