Describe the sound that Watson hears?

From the text:

As if in answer to his words there rose suddenly out of the vast gloom of the moor that strange cry which I had already heard upon the borders of the great Grimpen Mire. It came with the wind through the silence of the night, a long, deep mutter then a rising howl, and then the sad moan in which it died away. Again and again it sounded, the whole air throbbing with it, strident, wild, and menacing.