Try adding the Blur and Sharpen>Directional Blur effect and apply the following expressions to its two properties:
To Direction: wiggle(3, 360)
To Blur Length: wiggle (3, 100)
To adjust the effect, change the numbers inside the parenthesis. The first number (3) is the number of random changes to Direction and Blur per second. The second number set (360 and 100) is the magnitude of change. The number 360 for direction means that the blur can be in any compass direction. The number 100 for Blur Length means that the blur can be a smear of 100 pixels maximum.