check the check straps, sometimes the balls get stuck. They are cheap enough where you should just replace them. i think that there is a thing in DIY on those.
What happens is they usually break the pin that goes into the body then it makes a loud pop which is really annoying.
Try this and other recomendations
No Benzes in the stable at the moment, but itching for one again.
Former Mercedes in the Stable:
1983 300CD Turbo diesel 515k mi sold
1984 300CD Turbo Diesel 150 k mi sold
1982 300D Turbo Diesel 225 sold
1987 300D Turbo Diesel 255k mi sold
1988 300 CE AMG Hammer 15k mi sold
1986 300E Amg Hammer 88k mi sold
1992 500E 156k mi sold