The cultural movement known as hip hop got its start in the 1970s, with African-American disc jockeys talking over dance music, trying to outdo other DJs. But the rhymes these rappers created also exposed the raw anger and frustration that was a growing force on city streets. Now, rap's relentless beat has found its way into homes all over the country and abroad, and onto the Billboard charts. Today the Monitor continues a series of talks with rappers who have made their mark.* NOV. 4: Queen Latifah. * TODAY: Ice-T takes music to its abrasive limits. * FRIDAY: The multiracial group 3rd Bass aims for rap that agitates for change but still makes people want to dance.