Apply the following expression to a Scale property to make a layer wobble at each marker:

  n = 0; 
  t = 0;
  if (marker.numKeys > 0){
      n = marker.nearestKey(time).index;
      if (marker.key(n).time > time) n--;
  }
  if (n > 0) t = time - marker.key(n).time;
   
  amp = 15;
  freq = 5;
  decay = 3.0;
   
  angle = freq * 2 * Math.PI * t;
  scaleFact = (100 + amp * Math.sin(angle) / Math.exp(decay * t)) / 100;
  [value[0] * scaleFact, value[1] / scaleFact];