A soft, murmuring, rustling, or whispering sound, like the wind in the trees or the sea on the shore.
The word 'sough' makes people think of calm, nature, and peace.
Examples:
The sough of the wind in the trees is very calming.
I love to listen to the sough of the waves at the beach.
The sough of the leaves in the wind is very peaceful.
The sough of the wind in the trees sounds like a quiet song.
The sough of the wind in the trees is like a lullaby.
The sough of the wind in the trees is the sound of nature's music.