A teen "Talk Radio," or "Good Morning, Vietnam" set in the suburban jungle, "Pump Up the Volume" isn't a particularly well-made movie, but its heart is in the right place. Precociously sardonic Christian ("Heathers") Slater plays Mark Hunter, a painfully shy New York-to-Arizona high school transplant with a secret life -- a "pirate" shortwave radio station in his basement from which he, as alter ego Happy Harry, plays forbidden records (there's a strong subtext about First Amendment rights), reads lovelorn letters from listeners and generally unleashes his raging teenage id. Happy Harry becomes a cult hero to the disaffected, alienated, repressed-on-all-sides kids (shades of "Footloose"), but he really riles the grownups. "Pump" is at its best when Harry and his listeners are talking, and it sensitively airs some particularly touchy teen topics. But writer/director Allan Moyle's screenplay is cloddishly heavy-handed when it comes to the parents, teachers and other authority figures, and a bogus subplot about an evil school principal manipulating SAT scores is unneccesary. When Mark and his black-clad admirer Nora (Samantha Mathis, as this movie's Winona Ryder substitute) take the show on the road -- they're on the lam from the FCC -- "Pump" finds the exhilarating pulse of healthy rebellion. As a side effect, this movie just might make radio and records -- remember? the old-fashioned, black vinyl kind? -- cool again. Area theaters.