Route 999

"The sound kept going on, throbbling quietly but insistent, it went like tsss hump pshaw gooo — it was not a bird or some other animal as I had first thought, nor was my imagination playing a trick on me, what was it then – a thought crossed my mind: was someone trying to communicate with me (I was alone, there was no one else around) in some sort of coded language? Occasionally the wind would blow in my direction and bring the sound closer to my ears."