Benn Jordan (The Flashbulb) has a series of videos where he goes to remote locations to record ambiance without noise pollution, a disappearing sound. https://www.youtube.com/watch?v=I1i_ECeB2fo
Yellowstone: https://www.nps.gov/yell/learn/photosmultimedia/soundlibrary...
Rocky Mountain National Park: https://www.nps.gov/romo/learn/photosmultimedia/soundlibrary...