When I first heard this I absolutely got goosebumps on my arms, this is the exact same sound I heard the night I was "whistled" at. It only lasts a total of 46 seconds, out of hours of audio.
You will need to turn the volume up high to hear it. The periodical mechanical sound is the internal camera noise. I started recording Saturday night before going to sleep and left it running until I got up the next morning. The time would have been up after 6:00 before the sun is completely up. I had been reviewing the audio over the past couple days and today discovered this while sifting through it, and was totally surprised to say the least. I have added a caption during the seconds when the voices can be heard, although it's near impossible for me to make anything out.