It’s a kick watching Meryl Streep rock out on guitar and vocals in Ricki and the Flash. Streep’s Ricki Rendazzo dumps her family to play bars with the Flash, a cover band made of bona fide musicians. That’s drummer Joe Vitale, keyboardist Bernie Worrell and bassist Rick Rosas, with Rick Springfield on guitar to play lover-boy Greg. Ricki is no star, and director Jonathan Demme, with music in his DNA, offers a heartfelt salute to those who play the underside of rock & roll because, well, they have to. Too bad the rest of the movie, with a script by Diablo Cody, is dime-a-dozen family soap opera. It helps that Kevin Kline excels as Ricki’s ex, and Mamie Gummer, Streep’s real-life daughter, imbues the fictional version with rare grit and grace. Otherwise, too many wrong notes.