I was listening to the Seven Lions track, Fractals, and was quite baffled by a couple of the sounds I was hearing. I have no idea how to describe them, so going with wind up for the first and wind down for the second seems to be the most accurate description.

Edit: In both clips, it appears like some extra audio got added to the beginning of the clips(even though it's not showing up in ableton), so the effect I am curious about is the one going on in the last half to two-thirds of both clips.