Sum and difference tones of A220 and unison, just perfect fifth, and octave. Note that this is not produced through ring modulation of two notes, but is four separate notes.
Last message in a series. This time lots of receivers around could download signal. Mathematics analysis could find two words from what seemed to contain advanced maps of some kind. The two words were : asteroid coming.
Sound of an empty soda can being dropped in an empty room. Natural reverb, only editing done was to remove the sounds of me walking around / picking the can up after drops.
Me shaking and turning a small cardboard box, mostly empty but still containing some nails and other metal bits. Recorded at my deskslightly edited to reduce background noise.