fast jet engined flypast
A mechanical clank, as of a cash register.
A recording of a particularly loudly humming lamp in a parking garage. Recorded with a Zoom H1.
Atmosphere: a river flowing, a bit more of the lows, giving it a roaring or maybe trafficky sound.
Bubble coming out of water
Different recordings of steam putting cold water on a hot pan/plate. Recorded with a Rode NTK (mono, 48kHz-24bit)