A dark Whirlwind nearby
Whirlwinds are very rare hostile mobs that were added in the v1.02 update to the Aether mod. Whirlwinds move about randomly, and can drop down or climb up. If a player gets too close to a Whirlwind, it will fling them into the air, like a zephyr would, potentially harming the player. Although Whirlwinds are considered hostile in this nature, they can still spawn on Peaceful mode. When they are killed they can drop a wide range of items and blocks (or random drops) like a continuum orb. They come in several colors, ranging from black to gray to white.
Note: Since Aether II Alpha, they have been removed, with no news on when (or if) they will be added again.