This is to follow up on my post. I went ahead and put in Dynamat and Dynapad around the wheel wells and in all 4 doors. This reduced the noise somewhat. However, the truly bothersome pounding noise still will occur on really chewed up pavement (asphalt or concrete, usually torn up from studded...
The road noise in my Leaf is very noticeable when I drive on pavement that has been chewed up by studded snowtires and I am driving at speeds over 30 mph. Since I commute on such at road for 9 miles each way at speeds between 45 and 60 mph, my ears ring terribly every time I get out of the car...