Recording natural phenomena?

You are heading in the right direction. You need to throw away most of the data and only keep the interesting bits. For you, the interesting bits are in a band of frequencies. Now you may want to write some software and use the sound card on a PC. You want to only keep the data where something pokes above the random noise.

No idea about the weird tone but it could be something like the ignition phase of a gas furnace. Newer ones have a little electronic HV generator that runs an arc for about 15 secs to make sure the flame starts when the propane or natural gas rushes in.

Maybe provide an amplifier somewhat away from the computer gear and differential feed.

When I did this, as a kid, I made a square loop antenna on a wooden x-frame, something like 50 or 100 turns, about a meter square. Stuck a cap across it and ran it into an audio amp. I heard a little hum, some obvious noise clicks, lots of presumed lightning, and the occasional very strange chirp/whistle thing.

I'd suggest a smaller loop, to just sample the local H-field without acquiring too much of the near-field junk from the motorcycle and such.

John

Digital voice recorders. You need to get away from the power mains. But filtering is done by some. Google for VLF natural radio, a portion of the amateur radio community does this.

I made a McGreevy receiver on a breadboard. Drive to a rural area. Listen with headphones.

Some links to get you started.