A question on Brian Eno's song Third Uncle

How did they create that harsh, jarring guitar tone? I’m talking about the riff that is first played near the end of the song (starts around 3:15, the song is about 4:47 long). It doesn’t sound like your ordinary feedback to me so I’m very curious. My friend who plays the electric guitar says they somehow processed (or raped, as my friend fittingly put it) the sound after recording it (probably true since the live recording I’ve heard doesn’t even attempt to reproduce the effect). How?