I've posted about this before, but highlighting it now: I'm reasonably sure that Glenn Branca's never-released fourth symphony can be heard at this mis-labeled show at the Internet Archive...and it's a banger: archive.org/details/Bran...

Glenn Branca Live - 1983-05-14 Houdini, Zürich, Switzerland : Glenn Branca : Free Download, Borrow, and Streaming : Internet Archive

A very good recording of a piece by modern classical innovator Glenn Branca - lots of droning and ambient harmonics from his loud guitar band as they play...

There are three movements here, though Glenn's site lists it as having four. One of the live recordings of it was supposed to come out on Atavistic in 2016, but to my knowledge did not.