I had some heavier work done on my car of recent, (water pump and belt tension system) and I have this... Droning noise coming from the front leftish side of the car, It honestly sounds like a cessna powering up for a takeoff, it is RPM dependant and is absolutely hideous around 2200-2500RPM (a little after the air and other ambient noise takes over) for the life of me I cant figure out where it's coming from, it's the front, and left side of the engine. the mounts look good, all my bushings/Mounts all were looked at under a week ago by myself and a mechanic.... This is all I've had done

• Belt tension spring and shock
• brakes
• belt
• Water pump
• thermostat
• thermostat housing
• Idler pulley (old one had a fair amount of flat spots in it)

I'm at a loss to know whats causing the buzzing. the car runs spectacular and hauls butt... this is one of the last few issues I have right now with it and I'd love to get it cleared out of the way.. any ideas?


also it's worth a note, the new belt squalls like two geriatric cats making whoopie......another annoyance

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed

Power steering pump... This may also be the source of your belt noise. Also, take a look at the belt alignment and make sure it's sitting properly on the 50 (not really) or so pullies it goes around...

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-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

Does it make the noise if you rev the engine in neutral? If not, could be a wheel bearing.

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Ed
-1984 Mercedes 190D 2.2 5-speed gray market(bought@30,000 miles) (Sold back to original owner@170,000 miles)
-1999 Mercedes E300DT (245,000 miles)
-1999 Mercedes S500 Grand Edition (80,000 miles)

When the shifter bushing is completely gone there is a definite buzzing. In my mind it does not elevate to a droning but is easy to check.

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1999 Mercedes E300TD daily driver sold at 238K miles 106K miles were mine, rust worm got it :-(
2006 Mercedes CDI new daily driver! 56,000 miles May 2016 now 85,625 Apr 2018 and Apr 2019 101,000 miles Apr 2020 109,875. March 2024 135,250

I hope it's not the pump.... That sounds like another nasty and expensive repair.... The sound is present when the engine revs in neutral, and it's not the shifter bushings. I've had a couple that needed those

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed

In my experience, the pump makes a low howling sound if the level falls even a mm or 2 below the minimum. There's also a steering fluid filter buried in there somewhere that may be restricted.

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-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

I will try to get a video of it today. And post it

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed

Drop tension on the belt and fire it up. If the sound disappears it will confirm it is IS a belt driven accessory device causing the noise.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

Untitled 04771366 - YouTube I hope the noise comes through... As annoying as it is in the video it's about 20x worse when it resonates in the cabin... Sound comes from the left side of the engine (drivers side)

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed

Sound can clearly be heard in your video. Was the sound present prior to the work you described being done? I am not questioning the quality of work your mechanic did, but you mentioned your tensioner shock being replaced. Prior to installing the shock, you are supposed to work the shock in and out all the way a few times before installing it.The fact that your new belt squeals could be an indication that the shock was not worked in and out fully prior to installation, and is not performing as designed in keeping the proper tension on the belt. Another possibility might be that the belt is not the correct size, or has a manufactures defect that is causing a harmonic vibration in direct relationship to engine RPMs. Good luck!!

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96 E300d

On the belt tensioner shock, did you happen to use a OEM Mercedes or aftermarket part?

I found the aftermarket shock to be very stiff compared to the one coming off, and wonder if there is a difference in manufacturing.

One thing you could try that would isolate the problem is to take the belt off and run the car briefly. Not much fun to do but would confirm if the belt system is the issue.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

It diddnt do it at first, when the water pump crapped out just before that's when the buzzing started...

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed

all parts were Mercedes parts, nothing aftermarket.

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed

Sounds rather "hollow".. Are all of the intake tubes in place?

Remove the belt and report back

Does the sound change when A/C compressor is engaged?

Take off the belt and check all the pulleys you can by hand.

I'm going to be the dark horse and bet on the A/C compressor and/or clutch.

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2005 Pathfinder LE
2001 E55
1998 M3
1982 320i