The Sounds Of Silent DesCent 

Many are aware of John Cage's avant-garde composition 4'33" from 1952. Probably the most famous 'silent' piece of music, isn't actually silent. The notion of the piece being that listeners tune into the ambient sounds around them during the performance of the piece. The length of 4 minutes and 33 seconds is the length of time the piece in three-movements was first performed. However, whether inspired by Cage or not, there are many weird pieces of 'music' that are aural spaces of total silence. 
In 1959 the University of Detroit had 3 silent records added to its jukebox, so that students could buy a few minutes of silence. The story goes that the records were so popular, that over time the 3 records developed scratches, so were no longer silent. John Lennon and Yoko Ono released an avant-garde album Unfinished Music No.2: Life With The Lions (1969), which contained a tribute to Cage's 4'33". Although the track '2 Minutes Of Silence' was just that, 2 minutes of total silence! In 1973, Lennon added another silent track to his 4th studio album Mind Games. Nutopian International Anthem was 3 seconds of silence at the end of side-1 of the album, a political statement referring to the conceptual country of Nutopia created by Lennon and Ono on April Fools Day 1973. Silent 'music' moved from being an avant-garde art statement to a political statement. The following article is a list of 5 key albums and artists that used silent tracks to make a political statement.
Before Lennon's use of silence on vinyl, a year before in 1968, The West Coast Pop Art Experimental Band released their psychedelic rock album Volume 3: A Child's Guide To Good And Evil. The final track on the album was 2 minutes of silence entitled Anniversary Of World War III. Bob Markley the bands lead singer is credited sleeve notes for the the track (despite it being 2 minutes of silence), which followed his political anti-war stance from previous albums. The album is considered the high-point of the band's career, and has been listed as one of the best psychedelic albums of all time. The band broke-up in 1970.
In 1971 Sly And The Family Stone released their fifth studio album, the classic There's A Riot Goin' On. The title track, which was listed as being at the end of side-1 technically runs for 0:00. So essentially doesn't exist. In July 1970 there were riots in Chicago, which were later blamed on the band not appearing for a concert as scheduled in Grant Park. The reason for the track, and why it essentially doesn't exist was explained by Sly Stone in 1997. He said the reason the track had a 'zero' running time was that, "I felt there should be no riots". The album is often listed, as one of the greatest albums of all time.
In 1978 the English anarcho-punk band Crass released their first album The Feeding Of The Five Thousand. (The album was actually an 18-track EP). There were objections to the controversial track Asylum, which in protest the band removed and replaced with 2 minutes of silence called The Sound Of Free Speech. The track They've Got A Bomb also contained a silent interlude, inspired by Cage's famous composition. The reason for this given, that the audience could confront themselves in the moment of silence, and contemplate the ever present nuclear threat that hung-over the world at the time.
Using silent records as political statements reached a peak in 1980, when the UK independent record label Stiff (under the sub-label Magic Records) released the totally silent album The Wit And Wisdom Of Ronald Reagan. The album that is said to have sold some 30,000 copies. The vinyl was pressed in such a way that is looked at a glance as if there was actual sound recorded on the album. There was no indication whatsoever that the whole album was completely silent. However it did cheekily carry the message "Warning: You may or may not hear something interesting on this record." 
Snivilisation (1994) was the third album by UK electronic dance music act Orbital,  contained the track Are We Here? In the same year that the UK government introduced the Criminal Justice Bill, which tried to ban the free-party rave scene that was spreading across the country. The bill specifically targeted gatherings of more than 20 people, where 'repetitive beats' were being played. Artists brought out protest tunes and albums. Prodigy's album Music For A Jilted Generation for example.  However Orbital were subtle in their response. Their remix of Are We Here? (Criminal Justice Bill Remix), ended with 4 minutes of silence.
During the early 80s at the height of the paranoia about Satanic messages in records, it was claimed that there were messages hidden in blank cassette tapes. Some teenagers locked themselves in their bedrooms and cranked up the volume, in an attempt to hear these hidden messages. How long they lasted, before they realised in whole idea was utter nonsense is anyone's guess.
Danger Music! Music Designed To Cause Pain - From conceptual art to viseral physical acts of destruction, Danger Music is a Dadaist genre of music that pushes boundaries.