Rock Cloud

>I have guessed that it is the result of sloppy tuning and
>loud thick harmonics. Its really a cool sound.

I don't think sloppy tuning is necessary; in fact, pure otonal tuning a
la Glenn Branca may be the best way to achieve this effect, since
distortion and loud volumes create lots of difference and sum tones,
which will all be part of one big otonal chord.