Today I noticed an odd beeping that appears to come from the passenger side of my 1998 CLK 320. It only happens when I turn off the ignition fully or turn the key off from the second position. It's 3 groups of 3 beeps. There are no warning lights on the dash or any other malfunction. In all other respects the car is running great. It seems to be coming from inside the glove box or passenger side dash panel. Any ideas?