SobRogue

So, I still have an ongoing issue with a noise on a 2010 C300 that arbitrary happens, and I/dealer can't seem to nail it down... It's been almost 10months, but still haven't gotten to the bottom of it

In the dealerships fairness the transmission was what making the initial load noise, which has been resolved, but there is still this just noticeable whistle/hum (almost sounds like someone circulating their finger on the rim of a wine class) -which is very irritating!

I've read many post about noises for this car that seem to be similar to what I have, but it's all text, and hard to gauge the exact type of noise. So I've attached two audio files, in hopes of finally getting to the bottom of it.

The phone picked up alot of static/road noise, but you should be able to pick up the whistle noises.

Also, the following have been replaced: transmission, front differential (3x), the rear differential, all front speakers (No idea rational behind this), new tires, tension pulley, and idle wheel...

Thanks,

Carsy

I have a whistle type noise which is emitted from my AC when it is lightly load ie a cool day.

It is not there with the A/C turned off (after about two minutes)

SobRogue

I have not been using the A/C, I do leave it on 'Auto', but explicitly turn the A/C off. I've been using heat though, it's been about 10-32deg F outside.

I tried today, and left off all climate control for ~20minutes, and the noise persisted.

The noise is somewhat intermittent, I can consistently reproduce it driving above 30-50mph with a light load, but under that, and at idle/revving, it only happens sometimes.

SobRogue

Here is a much better sound bite-

This is on a cold start, at idle with all climate control turned off.

The car is not in gear, but if I do put it in gear, the sound starts to flutter like in the first sound files.

Carsy

Its a mystery especially with new tires, tension pulley, and idle wheel replaced.

Try a small amount of silicone spray on your serpentine belt to see whether it quietens it.

SobRogue

I'm not sure the tension pulley actually works correctly, despite the dealerships assurance to me.
I would have assumed the tension pulley itself would remain in one spot under tension, but the new one moves 2-3mm constantly back and forth under the spring arm. Is this normal, or could this be causing the noise?

My only other guess, is that the noise appears to be coming from the front of the engine on the passenger side, near the pulleys/belt. I see the alternator, but what else is located on that side?

Carsy

I do not have your engine so cannot say a whether the pulley should move. I suggest that it would move slightly with change of load & speed. The tensioner on my diesel is still.

The noise you describe could be a bearing. Alternator as you say. You can buy an auto stethoscope cheaply & I suggest you move it around suspect spots ( bearings, gears))especially when the noise is present.

Be careful not to come into contact with belts , rotating gear & electrical terminals.

Good luck & keep us posted.

nelson g

Instead of buying a stethoscope an old mechanic showed me how to use a wood yard stick as one. You place one end on the front of the pulley and you place your ear on the other end and sure enough you will hear if it is the bearing.

I have to say once and awhile I hear the same noise from my C300. I can't tell if it a little moisture on the belt or the bearing in one of the pulleys.

SobRogue

The car has been at the dealership for literally more than a month -36days... and still nothing to show.

They have additionally replaced the engine mounts and pins(no idea where/what these are). But the noise is still there, in fact it's gotten a little worse -so frustrating!

Their findings are that they hear and acknowledge the cabin noise, but can't reproduce it in dyno-mode, and thus can't do anything. More than a month, of work, for this, How useless can you get!?

I've ordered a mechanics stethoscope, and am probably just going to buy a new serpentine belt. Any other ideas?

I've spent all day playing around with the noise, and it is definitely not the transmission, because if you put it into neutral (while driving), the noise is still there. I'm also not able to reproduce it sitting idle. So the noise only appears if the car is in motion. Although I just barley hear a constant pitch if I stick my head in front of the belts...Thoughts?

Carsy

A forum member had a noise he could not track down. Turned out to be a drive shaft bearing.

https://mbworld.org/forums/c-class-w...ease-help.html

Take out your back seat to see whether it sounds louder.

deuce40s

In your post #4, does that audio have the whine sitting still at idle? That's the way it reads.

Does the noise change pitch or remain constant? Fuel pumps make whining noises. I don't know if we have in-tank or in-line pumps, but find it and put your ear to it.

You said you replaced the front speakers, but have you replaced the rear? At least unplug them to make sure no interference is coming through, free test. The sound may come from the front, but it could originate from the rear.

Lastly, if you really think it's coming from a pulley, spray a shot of WD-40 on one at a time (not the belt surface), and see what happens.

SobRogue

Ok, I read the the dealer report, supposedly, they did a static (sound?) analysis on the rear axle, and frame and where not able to hear a noise. Could it still be the drive shaft bearing?


Recording 4 is at idle, but that noise is only reproducible on a cold start now, and disappears after warming up -maybe it's still related??

The pitch remains more or less the same, maybe a little change, but it whines louder/softer when it happens. Where is the fuel pump, is it under the rear seats like most cars? (Is this your suggestion Carsy?)


Either way, I'll try unplugging the rear speakers - I don't think it's related as the dealership hinted that that was an error on their part and they were mistakenly replaced (intended for another car).

The stethoscope will arrive tomorrow, I will give that a try, before oiling each pulley -although I'm not entirely convinced this is the issue anymore.

I will try taking the rear seats out at some point, but this is a weekend project. Is there a DIY for this?


Thanks for the help.

deuce40s

I almost immediately suggested checking the speakers but reread your OP and saw you did that already. Speakers can do funny things.

The fuel pump is in the tank so crawl under the car and put your stethoscope right on the tank to see if you can hear it. Some pumps are louder than others. It's just another free test.

SobRogue

It's hard to tell, but the noise may in fact be coming from the alternator. (I guess similar to one of the posts in the link Carsy linked).

Although, I'm not sure -as I have nothing to compare it to. Using the stethoscope, there is a high pitch, rumbly whine. It's hard to tell if its the same noise, as the car was at idle, and the audible cabin noise only really occurs while in motion.

I point this out, because if I listen to the center bolts of either the tensioner, or idle pulley, there is no obvious noise -other then the ticking of the spinning wheels. Where as the alternator is 'high pitched'. Could this be it?

Are there any other ways of testing this, or does someone know what a good alternator sounds like?

Also, for completeness, I put some silicone paste one the belt with no change, and when listening to the gas tank, I hear a 'liquid' whooshing/sucking noise -not a whine as I hear in the cabin.

Carsy

You could investigate running the engine briefly without the serpentine belt. Remember no power steering or coolant pump.

SobRogue

I just picked the the car up again from the dealer. They have done a full diagnosis of the Alternator, and have ruled it out...

This is frustrating, they acknowledge the noise as a fault, but are also trying to pawn it off as a 'normal' wear noise -but I'm not buying their bs...

Anyway, I had someone else drive it home, while I used the stethoscope, and I think I may have another lead... another bad transfer case. The transmission has already been replaced, and has less then 2000miles on it!!!

Anyway, I've pried off the top cover of the shift plate (The cover with the P, R, N, D -I'm not sure what it is called), and the noise is much much louder, and at slower speeds. The stethoscope picks up the noise, and it's very apparent.

Back to the dealer...but I'm am now concerned that they are going to dispute replacing it, with some sort of rant about there being no functional issue, even though replacing it should be covered under their part warranty.

Any one have experience, guidance, or suggestions?

Carsy

Well done on the diagnosis.

Leave the cover off & ask the tech whether he needs a hearing aid.

Good luck.

SobRogue

More then a year later, and the issue has finally been fixed! I thought I'd close out and advise anyone else with similar symptoms.

Coincidentally, and by pure luck, I stumbled across an independent MB specialist while on a detour to work one day- and I was open to a 2nd opinion.
In short, they were more in the business of restoring older cars -but, they advised me to go to another dealership who they partnered with. In fact, they even scheduled the appointment for me. (I was actually skeptical, I don't know very many places to defer business).

I took one ride with the mechanic, and he knew the issue was a shift rod mechanism immediately.

There was even a Technical Bulletin for it, LI27.60-P-049151. I guess this is the shift rod head and floor shift assembly. After replacing these and the bracket/assembly that hold them, the noise was finally gone!

I will no longer be using the previous dealership. The fact that a technical bulletin existed, and they still couldn't fix the issue, sorta smells a little like warranty fraud to keep their service department busy...or incompetence at the very least.