The sound was something I had not thought of, but yes, when the wind blows harder, they flap in the wind like flags and make a similar snapping noise. Very interesting. I thought the size was about right. I found them to be most intersting when they are on paths that curved and changed in elevation. From a distance they change quote a bit depending on the wind.
see this thread for pics I took today:
http://www.freerepublic.com/focus/f-bloggers/1342111/posts
Great pics. Thanks for the observations too. Interesting that he earns quite a bit from his drawings...and his drawings are quite good, clearly showing a draftsman's skills; this flies in the face of those who assume he cannot draw if his life depended on it or that he doesn't make money "the old fashioned way."