Unknown Radio Broadcast 1970

*Not a Sighting*.  I recorded something off  AM radio in 1970, when I was 10 years old.  Unfortunately it was on cassette tape and the thing broke years ago, (it's gone/lost).  It went on for about a half hour before I couldn't stand listening any longer.  
The next time I turned on the radio a normal sounding, (Chicago?), symphonic station was playing.  I haven't heard anything like it before, or since that time. It was very scary, repetitive, yet always different. I think it must have been some form of music.  There was some kind of pig creature talking/or perhaps singing.  It made a guttural sound that no human could possibly make, (it sounded like it had a massive chest cavity).  
In the background was a constant overwhelming clanging, coupled with a buzzing that seemed to fade in and out.  Occasionally I could pick out what sounded like human screams in the background.  Like someone in excruciating pain, or someone suddenly facing some dreadful unavoidable consequence.  There was tons of ambiance.  Ambiance everywhere, in the pig man's voice, the buzzing and clanging, even in the screams buried far off in the background somewhere.  
I know the AM band can skip, but I have to believe this was something different.  It was either a very strange broadcast for 1970 and the radio station it was found on; or was it something beyond this world?   I am sorry I do not know what frequency it was.  
My dad changed the station to listen to the WGN grain prices.  I remember the radio station indicator being slightly right of center, I'm sorry I cannot be more specific.  I would definitely recognize this if I could hear it again.  The problem is, it seems to be gone, and it has been 41 years now.
Witness indicates that the date of the sighting is approximate.  PD