The noise...

I have never been to a rough pebble/large rock beach before.  I went there today and the noise was so fascinating.  It wasn't when the tide waves came in or when they crashed on shore.  It was when they washed back out to sea.  I don't know how to describe it other then to say that it sounded like millions of rocks moving in one motion.  I wish I could find a youtube clip of it and I would post it.  If I ever find myself in Lima again I will record it.  Tres interesante.