Thanks for the info.
I'm not sure when it started getting worse. I usually have the radio and A/C on and the windows closed, so I wouldn't often hear it. My A/C died about a week ago and now I've usually got the windows down. But the other day when I was accelerating on an uphill freeway onramp with a soundwall, the rattling bounced off the wall into my window and really caught my attention.
The EZL module; is that the ignition control unit mounted on the driver's side inside fender well? If so, I did have to have it replaced about a month ago. The original one just up and died with no warning at all. I took the car to a local reputable independent Mercedes shop and they replaced it with one from a salvage yard. The number on the original unit is 004 545 44 32 and on the replacement part it's 006 545 76 32. I was told that they were interchangeable. Can anyone confirm this?