The son of Police Chief Wiggum is chosen by a music producer to record songs containing subliminal messages about what? 
New Kids on the Blecch:  In the episode, a music producer selects Bart, Nelson, Milhouse and Ralph to be members of the next hit boy band, who record songs containing subliminal messages about joining the Navy. Ralph Wiggum:  The son of Police Chief Wiggum and a classmate of Lisa Simpson, Ralph is best known as the show's resident oddball, and is noted for his non sequiturs and erratic behavior.
joining the Navy