Only happened twice in the last couple days. When the car (83 300D)is accelerating from a stop, normally in second gear, just before the shift to third would normally occur, I feel and kind of hear a low rumbling. It only happens if I am going up a slight hill (think inclined bridge or on-ramp) If I press harder on the accelerator it rumbles harder but not too bad. Each time it does it, the tach needle stays steady and the engine sound does not sound like it is revving excessively (and the car still accelerates normally).

Any ideas? I don't think the trans is slipping, but I cannot rule it out as it is the original with 276K on it. Trans fluid and filter were changed about 6,000 miles ago. The fluid does not look or smell burned and it is a the proper level on the dipstick.

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

Anyone??

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

Check the condition of the drive axles and flex discs.

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'83 300D, 126K miles.

Flex discs have about 50,000 miles on them and looked good when I checked them about a month ago (no cracks), but I will check them again. I'll have to check both rear drive axles. Anything specific to look for outside of excessive play an torn boots??

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

A wheel bearing?

Shot motor mount?

Fan hitting shroud?

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Cheers!
Scott McPhee

1987 300D

Because of the inherent noise/vibration, identifying/sourcing ancillary noise on a diesel machine is certainly a challenge!

First thoughts are to see if the noise can be heard/identified/ or is happening when at a standstill - regards the engine's RPM?

I used this method to identify that a noise occurring @ 1,800 RPM, just before my CDI diesel upshifts under easy acceleration, was ALSO happening identically at standstill. This revelation eliminated the transmission AND complete drivetrain from suspicion.

In my car's case it was occurring because of the worn engine mounts by vibration transmittal through the car's underside to the tinny, aluminum heat-shielding material MB uses on my car's underside. New engine mounts - problem noise solved.

Back to your car; worn engine mounts OR drivetrain parts, including possible worn rear half-shaft assemblies? A worn rear differential mount?? Wheel bearings? ANY other loose materials on the underside that may need tightening up?

First - see if the noise happens at standstill. Enlist a second set of ears as you advance the RPMs at a stop, free to walk around the car to listen for a source.