Hi,

I'm new to this forum, but I've recently acquired a 1983 Mercedes 300D TurboDiesel. It's got 180k on it, and seems in great shape for the most part.

I've had it for two days or so and recently I've noticed an infrequent noise at 50 or 60 mph. It sounds like a dull fast banging noise coming from under the drivers seat. Kind of like a helicopter, if you will. It lasts for 30 seconds or so and usually dramatically changing speed will make it go away. It's only happened twice in 300+miles of driving.

I've done my homework (a little) and I have some theories:

1. The carrier bearing/rubber mount on the driveshaft. I inspected this and it seems intact and with minimal slop.

2. the flex-discs. I inspected them and they seem intact and without cracking.

3. somewhere in the rear end, being telegraphed up the driveshaft? cv-joint wear or differential troubles?

4. something non-driveline related. Exhaust banging? Motor mounts? I'm fairly certain that the motor mounts are tired, based on the shake I get at idle.

Can anybody shed some light on this? Would the likely suspects of the carrier bearing or flex-discs be the culprit even though they look fine? I would love a few educated opinions before I start throwing money at this thing.

Thanks!!
Justin