My 83 300SD has a very odd rattling noise I am hoping someone can help identify.
The car has 350,000 miles and runs very strong but recently a loud rattle / knocking noise at idle and up to 1500 rpm regardless of load has me puzzled.
I was able to identify where the noise was coming from by using a stethoscope with a rubber hose. It was the loudest when placed into the inspection hole between the engine and trans.
I took it to my local import repair shop and with the car in the air found a cracked flex plate and a torque converter bolt sheared off, never seen that before.
I was positive this was causing my noise since it was exactly where the noise was the loudest.
I had the flex plate and the bolt replaced.
Installed the flex and the torque converter with all new bolts and.......the noise is still there, just as loud.

Has anyone ever heard of the torque converter making a rattling noise?
It has been suggested that the torque converter has play either internally where the input shaft fits or in the front pump of the trans where the converter flanges engage the pump.
I have no drive-ability issues at all, the trans shifts as it has for the 7 years I have owned the car.
The fluid is clean and has a new filter.