Most of the time Georgia Tech’s Rambling Wreck radio sounds like a three car pile up.  Even among college stations, its programming is considered extreme.  But stuck between “Concussion Theater” and a show called “Tongue Bath” is the station’s longest running program —  Fred Runde’s Desoto Hour — the show with the most listeners.  The 77-year-old disc jockey is not a Georgia Tech student.  Nor a teacher.  Never was.  He’s been spinning Big Band magic here since Jimmy Carter was in the White House.  Fred wandered through the door looking for something to do in retirement.  Students swooned for his oasis of sound.  Runde believes that noise is merely music someone doesn’t want to hear.