We caught up with Machine Head front man Robb Flynn last week at Green Day's Jingletown Studios, where he was putting the finishing touches on the Grammy-nominated Oakland group's upcoming seventh studio album, "Unto the Locust." There was just one problem. "We can't seem to write a damn song under six minutes," he said. Flynn wasn't kidding: The band's latest single, "Locust," clocks in at over eight. Machine Head, by some estimates the second-biggest heavy metal act in the Bay Area, plays the main stage at the Mayhem Festival at Shoreline Amphitheatre next Sunday.