Yes the dinging sound is always on. Even when I take the key out of the ignition. I know on my other 2 benz 's when I take the key out I here and feel a little click. This car doesn't do that. I haven't had the problem with the car arming itself in about a week (basically because I never lock my doors and leave the keys in the car). But it still tells me to remove the key still dinging away even though it's out. The square key fits the ignition only. Doesn't fit the door, glove box or trunk. Round key only opens driver door nothing else. Now I'm even more confused.

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Current fleet-
2015 BMW 750i xDrive
2009 BMW 535i xDrive
2004 Chevy Avalanche 4x4
1993 Mercedes 300SD
1993 Mercedes 300SE (parts car)

Previous Benz's-
2001 Mercedes SL500
1983 Mercedes 300SD
1980 Mercedes 300TD
1996 Mercedes E300D
1999 E300DT
1984 300TD-T
1988 Mercedes 560SEL (parts car)
1979 300SD
2003 E500
2004 S430 4Matic
2001 E55
2003 E430