The sound made by a mole cricket (Gryllotalpa sp.).
These sounds were coming from just under the ground during a frog survey in Kadur, Karnataka. I had never heard the sound before, and it was quite eerie to hear it coming from very close to you and not knowing what was making it. The variety of assumptions I made at the time were wildly far-fetched - ranging from an unidentified amphibian call, to the sound of leaking irrigation pipes or faulty power lines!
Habitat: Areca plantation in a dry region (rain shadow east of the Western Ghats in Chikmagalur)
Distance: Less than 1 ft
Recorder: ASR Recorder on Android phone