1991 300SE, 175k miles.
When backing out the driveway, the tranny makes a clicking sound, almost like the parking pawl is semi-engaged.
Clicks about 3-4 times per second as the car slowly rolls back. Seems to be clicking maybe 3-4 times per driveshaft revolution. Does it every time.
I can just hear it with the windows up, but it's pretty distinctive with the window down or the door cracked open.

I got it on the lift, shifted to reverse and drug the brakes a bit, fiddled with throttle and brakes, and finally got it to make the sound.
- It's definitely coming from the tranny. Maybe the rear section, but difficult to tell. Sort of a metallic click, rattle, click, rattle about 3-4 times a second with the car idling in reverse.
- Occurs only when the driveshaft is turning, stops when you lock the brakes.
- Not the parking pawl, linkage is adjusted right, have to move the lever a ways into park before the pawl starts to click.
- Does not appear to be the flex disc or the center carrier bearing, both are pretty new. I know the sound can "phone" up the shaft, but i'm pretty convinced it's coming from the tranny.

Tranny is perfect otherwise, no leaks, perfect shifts, lots of fluid and filter changes in it's 17 year life.

Any thoughts or advice greatly appreciated.

Tks,
DG