Tighten your door check straps!
 

Or whatever they are called. My left rear door was sounding a bit funky when I closed it, which is admittedly rare because I'm usually driving by myself. The MB thunk was sounding a bit tinny.

I eyeballed the check strap where it goes into the door and dang if both bolts weren't hand loose! Tightened them and went door to door, and 3 of 4 doors had loose bolts... Only the driver's door, which of course I use all the time, was tight. Go figure.

The thunk is restored, thank goodness...

Rgds,
Chris W.
'95 E300D, 267K

Rear doors on my 380se both have bad door checks... slam legs when you try to get in... Has the parts, just has to get to some wrench time to fix a buncha little annoyances...

Nobody rides in the back seat, anyway, so there is no giant hurry... If someone does ride back there, will pretend I am a gentleman and hold the door open for them...

Resurrecting a 10 year-old thread. :D

I replaced my drivers-side check strap today. About 7 months ago, I had the same noise and two loose bolts (above and below the oval hole where the strap emerges from) described in the original post, and tightened them.

During the time they were loose, the metal feet/tabs those bolts screw into deformed. After tightening them, the deformation changed and the constant opening/closing of the door caused them to flex repeatedly and break off. At that point, only a single bolt was connecting the strap to the chassis; and the door would make two LOUD cracking sounds whenever it was opened.

It's a good bet that if your check strap bolts have been loose for some time, they are likely close to failure. Thankfully, it is one of the easiest, fastest and least costly repairs you can can do. ($25 for new strap and 20 minutes to replace.)

Mine ended up doing that on my front driver side. Every time I opened/closed it would pop like something was binding. I ended up zip tying it. Been good for about 3 years now.:D