When the wind blows, this tree sounds like a bubbling spring. The hulls of the nuts in the upper branches clack together and give the illusion that there is a little spring near by singing its heart out. [I included the second two pictures just so you could see the nut-hulls a little better].
As a matter of course, there are in fact several springs around the property. Some are hiding underground, others have been concealed with the surrounding development, and I believe that a few others are trickling their way through the trees, lost to all but the secretive deer.