CBS Radio Mystery Theater was a radio drama series created by Himan Brown that was broadcast on CBS affiliates from 1974 to 1982. 

I remember listening to these shows when I was a kid.  There are 1399 in all.  They are available on the web in many locations.  Most have been edited to remove commercials but some still contain not only commercials but also news broadcasts.  The hour always stared with a CBS news broadcast.  The recordings I have start with news about Watergate in the very first episode.