If 300 flashing lights and 150 babbling audio speakers inside a 1,400-foot traffic tunnel sounds like your idea of a good time, head on over to Park Avenue at 33rd Street this Saturday or next between 7:00 A.M. and 1:00 P.M. There you will find Voice Tunnel, by Mexican-born artist Rafael Lozano-Hemmer, a champion of free speech and rollicking times in public spaces. Part of the NYC Transportation Department’s Summer Streets program, the project allows all visitors to step up to a mid-tunnel microphone and make a brief statement to a roiling sonic mix that might remind you of a noisy restaurant, all under disco lights. Seldom is exercising your First Amendment rights so much fun.