I cannot find it on my 08 550 sport and some say it is yet some say it is not. Is the valve in the drivers or passenger muffler(referring to the two mufflers on the drivers side)? Is the mechanism for the valve located on the top or the side. I cannot see or feel anything on my car

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12 X5 50i Sport
11 M3 DCT
11 X5 50i (lemon)
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08 550i M-Sport
04 BMW 545I sport
07 BMW X5 4.8I sport
02 BMW X5 4.4i sport
01 BMW 540I M/sport
00 SL500
97 SL500