The bubbling sound of leaves

An interesting phenomenon this afternoon which I do not believe I have encountered before.  

I let my dog out mid-afternoon into the backyard.  I stand there waiting for her to return.  As I stand, I hear the soft plopping of raindrops.  Or almost of a bubbling fountain.

The sky is blue and cloudless, the sun is out.  There is no rain.

I listen closely and still the sound of falling drops.

There is no wind in the trees which sometimes simulates the murmuring sound of rainfall.  

Still that sound.  I am intrigued and stand rock still, listening with all my attention.

I finally figure it out.  Our trees are still largely green but autumn is definitely here with some leaves turning and falling.  

While there is not a wind, there is the barest of zephyrs, stirring the leaves very gently.  Just enough to dislodge some of the riper leaves, many of them not yet dried, only partially turned.  None of them dry, which cause a rustling sound.  No, these are still leaves with life in them, but departing life.  They no longer grasp their branches as firmly. 

The bubbling fountain sound are all these soft leaves falling and hitting flat surfaces such as roofs and porches.  A multitudinous plopping, for all the world sounding like gentle raindrops or bubbling water but only the sound of soft leaves falling before their time.