The HONK! Festival brings a cacophony of joyful — and free — noise to Somerville once again this weekend. This “festival of activist street bands” surges through Davis Square in its 6th annual campaign to reclaim the roads, with opening ceremonies kicked off by What Cheer? Brigade, Emperor Norton's Stationary Marching Band, Afrobrazil, and more. The HONK! parade (this year’s theme is “Share”) starts marching Sunday at noon, rain or shine, finishing up in Harvard Square.