I think a lot of it does have to do with the sound carrying so far on the water, we used to watch them on a small lake in central Florida and would actually take our boat within a couple of hundred yards of a straightaway and they didn't seem too terribly loud but yet whenever they are way out offshore you can hear them very well, just like you are saying.

I'm sure one of the smart guys will be along soon to give us the proper explanation.
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Rick
Our Room

smile