Martians Go Home (1989) on Netflix

Plot summary

Mark Devereaux spent years pursuing a jazz career and now writes themes for television shows and jingles for commercials, though he wants to write meaningful music. He wins a job scoring a science fiction film, and the producer asks for something that could work as a greeting to the universe. In a cabin over a weekend he writes a piece he thinks is worthwhile, then calls his girlfriend, who produces a talk radio show, and the song reaches the air by mistake. The next day a Martian appears and says they heard it.