Semi Active Muffler Valves (Naturally Aspirated Vehicles Only)
WARNING: This page is about a different car, the 2011 Jaguar XKR, 2011 Jaguar XK, 2010 Jaguar XKR, and 2010 Jaguar XK. However, it is still accessible from the selected car via links, so may be relevant.
At low engine speeds the SAM valves are closed and restrict the flow through the muffler, which produces a more refined exhaust sound. At higher engine speeds the increased pressure in the exhaust system opens the SAM valves and the increased flow through the muffler produces a sportier exhaust sound.