The feedback sound of Live At Pararararararamount.

I always wondered how Kurt achieved his guitar feedback on there. It seems very aggressive and kinda unstable/sudden/and really jittery (cant describe it any worse). For example the beginning of Negative Creep. I wondred if this is some combination of high gain,treble,loudness or something else involved? I didnt get the chance to experience a fully cranked amp yet so I dont really have experience.