A black disc jockey is harassed by an unknown person, who he never meets face to face, anyway he gets the police involved(I believe there were some murders). In the end you'll find out that the dj has a split personality disorder and was harassing himself. It's been a very long time since I saw this particular movie, so I can't remember the plot details and the little info I have here might be a bit off.
The era is probably from the 1980s-1990s.

Dead Air (http://www.imdb.com/title/tt0109562/)