A snap-action valve assembly for an exhaust system is provided with a conduit that defines an exhaust passageway. A valve flap is disposed within the exhaust passageway for controlling exhaust flow. A shaft supports the valve flap in the exhaust passageway and allows the valve flap to rotate between closed and open positions. A mass damper, positioned outside the conduit, includes a longitudinal segment that is rotatably coupled to the shaft and that extends between first and second coiled ends. The longitudinal segment includes an inboard side and an outboard side. The first and second coiled ends include a series of overlapping layers arranged in either a folded serpentine shape or a spiral shape.