Whining noise!
 

I have W205 C250 petrol unit with 7G-Tronic+ automatic tranny. During winter, a strange noise appeared, it sounds like whining. I think it gets worse as temperature drops. It's somewhere below the car, diff or PTO, cannot tell for sure. I've visited service and I've been told that crank's PTO center bearing has been replaced. But... the sound still remains. It is quieter, but the sound is still there. It happens between 55 and 60 km/h, around 84 km/h and around 175 km/h.

What it could be? I'm going nutts, especially because it seems they consider it fixed.

If it fades under acceleration and is louder when coasting I'd suspect the differential bearings are starting to fail.

On a car 1 year old? Jesus... I can say that sound is louder when you reach specific speed and release the pedal, but it lasts for a second. Otherwise, the sound is constant at specific speed. In other words, if you accelerate to 180, you will hear it at 175.

What is advice here? What to do? How much would it cost to replace diff bearings?

mine does this if i accelerate hard when the engine is cold in the winter, figured it was the tranny

I never push cold engine too hard. This must be related to some moving part, bearing or something. I will have to push them harder to find what it is.

It's unlikely but possible. They don't typically rebuild sealed parts. You'd get a new pumpkin under warranty.

I'm not sure if I have this too but I hear a whining kind of sound when I press on the gas aggressively(not WOT) and I lift off a bit to coast. This is all in D(not Manual and no paddle shifting). The engine has this whining sound, either that's how the engine sounds when it's coasting. It feels like it's trying to decide what gear to be in(usually around 4-6k RPM).

This is the sound I'm talking about
It is loudest around 9th or 10th second

FYI, it's rear differential.

Sadly this can happen on any car due to poor manufacturing/quality control/materials etc. My Z4 has been fine, but others on the Z4 forum have reported (and had replaced) whining diffs at varying mileage (some just a few thousand).

Seems that quality today is not the same as it was before. We pay 50K for these cars (or even more).

increasing demands and build to price...

Having said that back then they didn't have Internet forums to highlight the flaws. Mercedes make so many millions of these cars, faults are inevitable in a few, just like any other brand.

It's usually just a bad set of bearings but nobody rebuilds diffs or trannys for consumers. They'll take yours in as a core and give you a fresh reman'd unit. If my math is right you're under on miles. Is warranty handling it?

Well, I hope they will. It was a wrestling session so far, it took more than a month of back&forth... Now they want to open it, don't know why. I believe I will get new part after that. Stay tuned.

I went to another service for opinion, they recorded the sound, contacted support, and one day after, new diff is on the way! Unbelievable! It was just like that.

Difference between a good dealer and a bad one. I get on really well with both my BMW and MB Dealers. Yeah sometimes it takes an argument, but never heated and they usually do their best.

So I've gotten a sound since the first day inside the car between 71 and 73 mph Even with the radio off there is a notable Harmonic. I haven't been able to identify where it's coming from but it's very annoying

If it's coming from below the car, dealer should lift the car and roll the wheels. It's easy to identify what is it.

Yeah I've never known MB to want to pay a local shop to crack open a pumpkin for a bad bearing. Too great a chance of contamination. Glad it worked out.

That's what dealer said, they were asked to open it. Now, after attaching a new diff, guess what!? A noise still exists! It is not that loud as before, but it exists at the same speeds. I can clearly hear it. I'm afraid it will get louder over time. The dealer says it takes time for components to fit together, but I'm not sure what that means. Its only 6 months left and warranty will expire. I think this will have to be raised on a higher level because they clearly don't know or won't fix the problem. For the past 6 months since the noise has been reported, they took and returned the car regularly several times with explanation that issue has been fixed. The car spent a month in total at the service for the past 6 months, and noise still exist. I got a replacement car during that period only once. Now, when I complain more aggressively, they said the car has been driven hard and therefore, it has noises and issues. Can you believe that? They let me drive failed differential for 5 months without letting me know what is the source of the problem (another service diagnosed the issue and got diff approved in 1 day), and now I still have to fight to get rid of the noise?!? This is really unbelievable. Find the source of the noise and fix it! What would be the best move here? I'm not saying I've been driving the car like a baby, it's a sport limo in AMG-Line, looking like a bullet for Christ sake. They will make me lose confidence in the car. I still enjoy driving it, but the noise is sooo annoying I cannot explain how much.

It is fixed finally with new diff, no noise anymore. I went through a nightmare on Elm street to get it. But now I can see something else happening just after the diff is sorted out - the car shifts gears around 6600 rpm, well into the red zone! I know for sure that it was at 6200 max yesterday, just at the beginning of the red zone! Is this OK and is it safe?

They need to readapt your transmission.
It's not safe.

Why would they let me driving a car that needs transmission re-adapting, especially if it is not safe to drive it in that condition? Nobody warned me about changed transmission behavior. And guess what, the new differential started to make noise again! Unbelievable! As soon as the oil gets warmed up in the differential, the noise starts to be present. I think this is the case for a money back request, they keep me in the dark for months. The car is constantly at the service. Few more months and warranty will be bye bye. I'm not sure what I'm driving anymore.

What? :)

We have got an impersonator on the site.