A sound from Sigur Ros' new song

[zeta]

It's the one that starts at :20ish - a really harsh, low, metallic, kind of "BRAAANG!"

And it's repeated throughout the song at different points, and in different forms.

[Hircine]

sounds like when you get a moog and turn all the oscillators down and crank the filter's resonance, then feedback loop it.