Metal Machine Music by Lou Reed is what to put on headphones at work when the sales guys are yammering away at top volume (yay open plan!). It is literally nothing but noise, an hour of multiple layers of feedback. Reed was quite into the amphetamines at the time, and literally intended the album as a musical version of speeding off your nut. It's possibly one of the greatest musical trolls of all time. Of course, it's been vastly influential with people who like horrible noise music. The whole album's up on YouTube.