I had a similar experience, down at the waters edge at dusk waiting for interesting sounds, only to be eaten by mosquitos and so I started making my own noises after 30 minutes of silence...and wind noises :)
Amazing... yes and eerie. Reminds me of the sound we heard a few years back when I was working at Uni of Canterbury in New Zealand and we thought there had been an explosion in the Chemistry Dept or something. Turned out to be a meteorite hitting land very close to us. No damage or injury though, fortunately. Thanks for sharing!