What's that?
 

Well... I found a few months ago some strange Sonic Youth files on Soulseek...

One is called "Fucking Around (Live)", it's a part of the Master-Dik third track...

The second is bizarre... It's called Sonic Midlife Crisis and it's a sample of TV Shit Track 4 Thurston Introduction a bit sped up with some strange guitar sample repeating over it.

There is also one called Su Nioj, but it does not corresponds to the description I saw and it only lasts 31 seconds...

Last one is called Anthony Braxton Can Kiss My Trad Ass and I never listened to it.

Someone know what is it?

no idea. But "Su Nioj" is "Join Us" backwards.