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2005 C230 Sedan Black
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Discussion Starter · #1 ·
First post here and I did some searching, but found nothing.

I have a 2004 C230 Coupe and the last 2 weeks I noticed a "chirping" sound when I have the AC on. The sound only happens when the car is idling very low, or when the car is put in reverse. It's almost like the belt is starting to squeel, but then it doesn't. The noise does not happen when the AC is turned off. Once the car has been running for a little while the sound disappears. It's only when I first start the car that the sound is happening. I talked with the dealer and they told me to check the belt. I could only find one large serpentine belt and it appeared to be brand new. Could it be possible that the belt lost some tension? Is there more than one belt on the car? There is hardly any play in the belt, maybe only a 1/4 inch or so, so I assume that it's tight enough.
 

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Discussion Starter · #2 ·
Ok so I talked with the dealer a little more and they think it's the idler pulley. However, they spent 3 hours today trying to get it to make the sound and the car would not. They used a stethoscope on the pulley and others parts, and said everything sounded great. They are keeping the benz over night to try and replicate the sound first thing in the morning when it's cold....
 

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2000 Mercedes-Benz S500. Sold: 2000 C230K, Sold: 1997 Porsche 944S
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If it was me; I would have sprayed some Spray Lithium Grease on the Belts and Pulley BEFORE I took it to the Stealership. Belts dry out. I hose the engine down once a month so things dry out. A little wax here, some spray lube there, a smattering of grease here, helps to rejuvenate old, tired rubbers.
 

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It's actually a no-no to put any dressing or lubrication on serpentine belts. This was a common practice on v-belts but these new belts are different. The kinda chirping sounds like a worn/busted needle bearing in one of the idler pulleys. You can spray lubricant all you want but these are sealed bearings and spraying lubricant from the outside will only waste perfectly good lubricant. When it's making the noise you can use a mechanics stethescope (autozone or pep boys should sell these) to isolate which one. Remember, these are spinning so don't touch them while the engine is running, just get close enough to hear. You may want to use a paper towel cardboard center tube held to your ear to localize the noise. Also, it could be the a/c compressor it self, specially if fluid is low it can make a chirping noise.
 

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2005 C230 Sedan Black
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Discussion Starter · #5 ·
Hmm... So you're saying to recharge the AC and see it that helps? It's soo strange that the dealer cannot hear the sound, but as soon as I'm in a public place it makes all kinds of noise. The sound seems to be getting worse. I just finished paying $200 to have the dealer tell me they can't hear the noise.
 

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2005 C230 Sedan Black
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Discussion Starter · #6 ·
Ok here is an update everyone. I hope somewhere out there somebody knows! I recharged the AC, took it into a shop and nothing is wrong. There was no loss of refrigerant; they pulled a vacuum and nothing. So I'm back to step one. One thing I have noticed is that the noise gets worse, louder, and more often. It's now to the point when I'm sitting at a light it will constantly chirp. I put a new belt on so I know this is not the cause. Also last night, the AC was turned off and when I was parallel parking, it made the chirping. The wheels were cranked all the way causing a strain on the insides and the noise appeared... Does this sound like a pulley? Idler pulley? My theory is that when there is a load on the belt, the idler pulley may not have its full tension, therefore causing the belt to slip and chirp momentarily.... Thanks in advance.
 

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I used to hear a similar chirping noise on my '01 C240 w/85k. Replaced the idler pulley, noise was still there. My next suspect was a water pump and it was it. Turns out the propeller shaft was leaning against the wall and slowly eating it, thus making that chirping noise. Replaced the pump ($100) and the noise is gone. Good luck.
 

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Discussion Starter · #8 ·
mslc791 said:
I used to hear a similar chirping noise on my '01 C240 w/85k. Replaced the idler pulley, noise was still there. My next suspect was a water pump and it was it. Turns out the propeller shaft was leaning against the wall and slowly eating it, thus making that chirping noise. Replaced the pump ($100) and the noise is gone. Good luck.
Was the noise intermittent?
 

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2017 GLC 300 4Matic fully loaded... but for the heated steering wheel. Stupid previous owner! 😠
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Change the belt tensionner. They lose tension after a while, which will cause the belt to make a chirping sound when under load mostly at low RPM. Most belt manufacturers recommend replacing the tensioner with every belt change. I know a lot of people are thinking "It's a cash grab!" Although it may be true, it is a relatively inexpensive part and you will have the perfect opportunity to replace it once you remove the belt. If it still makes the noise after replacing the tensionner, the next step would be the idler pulley. But I suspect it is the tensionner.
 

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Discussion Starter · #11 ·
Whosdis said:
Change the belt tensionner. They lose tension after a while, which will cause the belt to make a chirping sound when under load mostly at low RPM. Most belt manufacturers recommend replacing the tensioner with every belt change. I know a lot of people are thinking "It's a cash grab!" Although it may be true, it is a relatively inexpensive part and you will have the perfect opportunity to replace it once you remove the belt. If it still makes the noise after replacing the tensionner, the next step would be the idler pulley. But I suspect it is the tensionner.
Ok thanks. I will go ahead and try it. Also, before I purchase this part I'm wondering if this is what I need.
 

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I have C-350 2006. I have been having the same problem with the noise. When its cold you hear it up front and goes away once the engine warms up. Lately this chirping noise comes when I put the car in drive and becomes faster as the car moves and disappears at some point. Have taken to the Benz dealership and have spent large sum of money, each time they fixed something else and charged decent amount of money. I am getting tired of it, sound is still there. Any suggestion or recommendation, I am all ears. Want to get in touch with me via e-mail, here is the address: [email protected].
Very much appreciated.
Thanks.
Tan
 
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