When Senon Williams isn't moonlighting as the bassist for Dengue Fever, you can find him plucking the low strings with the breezy psych-rockers Radar Bros. The Bros, who have produced a beautiful racket since 1995, are making their second appearance of a monthlong Echo residency tonight, in anticipation of their fifth studio album, Auditorium. They've done a good job keeping tracks from their new record on the down-low — that is, until now.