While one new Angels reliever (Ryan Madson) resumed his throwing program Monday morning, another (Sean Burnett) was shut down because of stiffness in his lower back, a condition Manager Mike Scioscia said he is “not overly concerned about.” Burnett, the former Washington Nationals left-hander who signed a two-year, $8-million deal with the Angels in December, left camp before the team began morning workouts to undergo an MRI test. He underwent surgery to remove bone spurs in his elbow in October. Madson, meanwhile, played catch for the first time since Feb. 1, when he developed soreness in his surgically repaired elbow after throwing off the mound for the fourth time this winter. The veteran right-hander, who signed a one-year, $3.5-million deal in November and is expected to be the team’s closer, will open the season on the disabled list, but the Angels hope he will be ready at some point in April.