c63er

So this morning on my way to work I stopped at a stop light and I heard a loud grinding sound along with some noticeable knocking/grinding feel in the floor. I put the car in neutral and it went away. Put it back in Drive and came back. I revved the car a bit in neutral, put it back in Drive and noise was back. The light turned green and I took off, the car feeling normal with no excessive or strange noises. I came to a stop at the next light and there was no noise while stopped this time. It still hasn't come back. It was very loud and noticeable when it happened. The fact that it was gear dependent (Drive vs neutral) tells me it's something internal, which is never fun (i.e damn expensive to even diagnose). I called a couple of shops that supposedly specialize in MB. They said they'd have to reproduce the sound in order to diagnose it. Sounds reasonable I guess. I just wanted to see if anyone else has experienced something similar.

Also, my car has been making a slight grinding/rubbing sound during hard acceleration. That might be a driveshaft bearing, but that obviously is the exact opposite, it happens only during hard acceleration.

Any feedback is appreciated.

Plutoe

If it were me I would run to a transmission shop or dealer!!

c63er

I called 3 shops. The most reasonable explanation I got was that it was a fluke and if it hasn't come back yet it was probably nothing and if it was anything serious the transmission would have gone in limp mode. Not a very satisfying explanation but I put about 70 miles on the car today and no sound or anything abnormal. This is very puzzling but they all said that if it can't be reproduced they can't do anything. The explanation that it was a "fluke" is beyond ridiculous.

c63er

It came back again and this time I recorded it.

https://www.youtube.com/watch?v=1faS...ature=youtu.be
https://www.youtube.com/watch?v=1faS...ature=youtu.be

C SEXY 3

I had this exact same thing happen to my car last week!!! Did you let your car warm up till 175?

Jasonoff

It's difficult to make out the type of sound in the vid. It's more of an oscillation sound. Possibly vibration through a mount? When you put it in gear it puts torque on the motor changing it's positioning.

If something is loose it could explain the intermittent noise.

BLKROKT

That doesn't sound like grinding to me. Just sounds like you're in Drive with your foot on the brake. It's going to sound different than Neutral.

c63er

It only happens in the morning and during the first 5-6 miles typically on my way to the gym. My gym is 5 miles from my house. I go at 5am so it's relatively cool at that time and the car is completely cold. It doesn't make the sound on my way back from the gym when I stop at stop lights, only on the way there. So yes, it's safe to say that the car is not at 175 degrees yet.

C SEXY 3

Bingo! Just let the car warm up and you are good!

c63er

It is hard to tell from th video but it's definitely like a loud knocking sound and feel that is in sync with the engine speed.

c63er

Aah no. This is not normal in any way, cold or warm.

BLKROKT

You ask for feedback and then say no that's not it. Clearly you don't know if it's normal or not, and the evidence that it goes away when warm is not enough for you. If you're so sure it's abnormal then just bring it to a dealer. Are you really looking for feedback or just someone to agree with you.

Jasonoff

You said it went away and came back. Was that mistaken for being temperature related?

Thermal expansion of parts can drastically change vibration levels in the cabin. When this bìtch is warmed up that block radiates a lot of heat. I have a thermal pic to prove it lol.

EDIT: really... they ***** out bìtch? What the fúck lol...

c63er

No, not the case here. I was asking if anyone else has had the same experience. Isn't that the whole point of forums, to learn from each other? I don't need anyone's confirmation. I was sharing in case someone else has already dealt with the same thing. I've had this car for nearly 30k miles now and it's only been doing this for the past month, on and off, but becoming more consistent. I know it's not a normal sound, I wasn't asking anyone to tell me if it is normal or not. I was asking if anyone has heard it before and what the culprit was. Now is it clear enough what I was asking in the first place?

BLKROKT

Not enough? Bring it to a dealer to diagnose. Cars make different sounds hot vs cold. Particularly this one. If you're so concerned just bring it in rather than posting audio and asking people on a forum to diagnose from that. How do you expect anyone to tell you exactly what it is from what you've posted. One person has already said that it just needs to be warmed up, and multiple people have said they don't hear anything unusual. You're asking for something here that's impossible to diagnose online dude

c63er

The question why is it doing it all of a sudden? And it's so loud that it would be hard to hear a person talking almost.

BLKROKT

Well that's tough for anyone to tell from what you've posted - I can't tell its that loud from the video. You really just need someone to look at it in person man, sorry. At least you know that you can replicate the sound when dead cold now.

c63er

Yep that seems to be the case. I was hoping that someone has dealt with the same thing and would share what the problem was so I can go directly to replacing whatever needs to be replaced rather than deal with diagnosing it from scratch. It's nothing that can be seen from under the car. It seems like the transmission needs to be separated from the motor to possibly see what the problem is. The only moving parts external to the motor, other than the crankshaft merging with the transmission in the back, are the pulleys on the front. They are not touching anywhere when in gear, I checked already. Sounds like some bearing inside. If this was a manual transmission car I would have bet a lot of money on the throw out bearing. Not the case here though.

BLKROKT

There are a couple of MB master techs on here who will probably chime in if they have any clue. Maybe one of the driveshaft bearings (does this happen while moving when cold or only when stopped)? Is there one on the output shaft, I don't know. Nothing comes up in a search.

Jasonoff

-Vibration at idle only in gear only when cold
-Vibration under load

That video has an oscillation sound (just like our engines heart beat), not a constant like you would have with something grinding.

Engine mounts are the likely culprit with the limited data provided...

C SEXY 3

This was what I was thinking also, engine mounts most likely but odd it's only when it's cold. I'll keep you all posted on my outcome

c63er

That's true. It's more of a dull knocking sound rather than a constant grinding. I guess I might replace the engine mounts just in case. I've looked at them before and I had a hard time imagining how I would get to the top bolts that go to the block. Any pointers from anyone who has done it?

C SEXY 3

ENGINE MOUNTS FOR SURE! Confirmed with my mechanic, I got a better video with the same exact sound as you. So get them replaced, 60k is about the time they go. Dad had the same problem, only happened in the morning in first gear while car was cold. Took it into dealer they replaced the motor mounts for $900.

c63er

I have 90k on mine. I called the dealership, they quoted me $1520 for both engine mounts and transmission mount. Pretty ridiculous but I have to decide if I want to deal with it myself or just pay for stuff to be done once in a while. I have always done any and all work on all my cars and don't trust anyone but it might be time to start doing so.

Mr. Lin

call a reputable indy shop that has experience with AMGs and see if they don't give you a better price.