It sounds like a jet engine, but not as loud. Very high-pitched. anyone know what this could be?

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1985 300D Turbo "Eunis"

possible low oil, suggest a change to synthetic.

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ASE Master Mechanic
https://whunter.carrd.co/

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
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Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
2003 Volvo V70

https://www.boldegoist.com/

Yep........what he said.........

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

Give that 3 year-old in the car seat a Tootsie Pop and see if that attenuates the whining for a while.



Sorry. That was a parenthood-induced reflex.

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1985 300SD, 203,000 miles, dark blue

Lil Sarah says: "Poor old Grandma Blue Car...She's sad."

you guys mean low diff oil? I would think it was wheel bearings.

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2002 VW Golf TDI-169,000 miles B20

I'd say it's a wheel bearing too. I had that happen on a front wheel a few years ago & that's exactly what it sounded like.

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Michael Roth

1982 300TDT Wagon
1982 240D Euro!, 4spd manual-Parts car now, dead engine
88 Jeep Grand Wagoneer-fixing up for offroading
1989 Ford F150 (rust bucket) For Sale!
1953 Dodge B-4F, 1 1/2 ton Stake Bed (new restoration project)

Get it on a hoist and start it up and put in gear and then start listining. Could be a carior bearing or the ring and pinion. You need to narow it down to where the noise is coming from

Put the wife in the trunk and drive around. She should be able to tell you if it is coming from the center or one of the wheels.

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Bill Reimels
Now down to one:
1972 300SE 3.5 W109 (Euro delivery)

Jack the rear up and see if their is any play in the bearings. That would tell you pretty fast what it is.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Rear end whining in high frequency is differential 99.999% sure.
Bearings are a grinding, rumble, growl or howl.

Checking the bearing play will hurt nothing and may find other issues before they are serious.

thanks. i'll change it tonight...i'm going to give synthetic a try. i've never changed diff oil before...what kind of oil do i put in there?

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1985 300D Turbo "Eunis"

I don't remember the size but you will need a big allen wrench. Also take out the top plug first!!! If the top will not come out stop; because if you drain the fluid and the top plug wont come out you now have a bigger problem.

I don't know the capacity on the W123 but on my W126 is is 1.2 quarts if I remember correctly. The manual should say in the back.

I recommend Mobil 1 75W-90, autozone has it for $8 a quart last I checked. Cheap insurance.

Whunter how often are you supposed to change the diff fluid? I will probably do mine every time I change the trans fluid. So every 30k?

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

The determination of "differential" or "wheel bearing" can be assisted if the following question can be answered:

Does the noise almost go away entirely when the drive shaft is unloaded?

The drive shaft is unloaded when you are cruising along at a steady speed and you lift your right foot ever so slightly so that the vehicle just begins to slow down. If you lift too far, the shaft will load up in the opposite direction and the noise may return.

Please attempt to reduce or eliminate the noise via your right foot, in the manner described, and report back.

When traveling at a steady rate any where from 40-65mph I get a high pitched noise. When I let off the fuel pedal the sound goes away and depress again and it returns. Is this bad wheel bearing? have something to do with drive shaft, differential?? Differential fluid has been changed, rear axles are new, rear brakes are new. This is my first post by the way.

heh... as of right now the car in question has been sitting for almost a year now... the water pump and t-stat need to be replaced and i have not had the time/money to do that, and i'm betting the fuel tank has a ton of algae growing it in now as well.

as far as the whine goes... i know it isn't the wheel bearings, and based on the old bimmer i'm driving now that has the exact same whine and has been officially diagnosed by a BMW specialist as a bad differential, i'm pretty sure that's the problem. i'm sick of trying to get rid of that damn whine though... i've done TWO diff swaps on her (they were both used, from silver star recycling), and the whine sounded slightly different with each swap. just my luck to a) buy two german cars with bad differentials (NEVER heard of those going bad unless they were abused by PO) b) buy a used differential that was also bad, and c) send it back, only to be sent another bad unit. gah... seriously.

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1985 300D Turbo "Eunis"