Not even unrelenting downpour could keep down the 11th annualHONK! Festival in Davis Square. The yearly nonprofitgathering of activist brass bands — this is, community-organized music groups with a social message — brought together 26 acts from around the world for a weekend of synchronized sounds. Groups ranging from Le Pompier Poney Club from Marseille, France toYes Ma'am Brass Band of Austin, Texas, played in designated street corners, community centers and green areas in Davis before lining up for a rainy march down Mass. Harvard Square on Sunday afternoon.