AND NOW HERE'S THE NEWS: Who says it isn't exciting working at Tower Records on Sunset Strip? Last Monday, it was almost impossible to get past the singles shelves without bumping into a pop luminary. Celebrity Shoppers included Bruce Springsteen, David Lee Roth, Molly Ringwald and Little Steven Van Zandt, who had a host of goodies under his arm, including a new Prince cassette. . . . Rap music is usually more attuned to current events, but the Twin City Rappers have concocted a fun (and obviously unauthorized) history lesson about the Minneapolis Sound on a new 12-inch single called "The Twin City Rapp (A True Story)." Written by Tim Lynch and David E. Ellis, it offers a concise sonic rap-up featuring profiles of Prince, Morris Day, Jesse Johnson and the bevy of funk-femmes who've recorded under the Purple One's auspices. (Our favorite couplet, praising Mr. Day, goes: "He's loaded with talent, that's a fact, or he wouldn't be signing movie contracts.") The song is available on Twin Town Records. . . . Philip Glass, whose new album is entitled "Songs From Liquid Days," will appear Monday at 2 p.m. on KCRW-FM's "Castaway's Choice," where he'll rhapsodize about his favorite records and chat with host John McNally. . . . And Black Sabbath has yet another new lead singer, 25-year-old Ray Gillen, who made his debut with the band last weekend at the New Haven Coliseum. Gillen replaces Glenn Hughes, who made a very sudden departure, citing "seriously strained vocal chords." Hughes replaced Ian Gillan several months earlier.