A valve assembly for an exhaust system of a vehicle comprises a housing defining an inlet, an outlet, and a longitudinally extending exhaust gas passageway in fluid communication with the inlet and the outlet. The valve assembly further comprises a valve flap disposed in the housing and rotatable between a first position restricting exhaust gas flow through the exhaust gas passageway, and a second position whereat exhaust gas flow through the exhaust gas passageway is less restricted. A mass damper is disposed within the exhaust gas passageway and attached to the valve flap. The mass damper includes end portions and an intermediate portion disposed between the end portions with the intermediate portion having a thickness that is greater than a thickness of the end portions. The mass damper is positioned proximate an inner surface of the housing and positioned between the valve flap and the housing when the valve flap is at the second position.