I know one of you is a mechanical genius! (Odd noise)

bauss

bauss

Active member
Jul 16, 2010
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All I want is the noise gone, I've surrendered and taken it in twice yet I never get a real answer, just theories of a bunch of shit to "try". Well I don't want to replace abunch of stuff that isn't causing the noise lol. So I'm trying to find some common denominators to narrow it down and I'd appreciate your opinions
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1999 mercedes c230 kompressor

In low rpms, gears 1-3, theres a intermittent noise depending how fast acceleration occurs (noise starts when acceleration occurs, [gas being pressed], rolling down a hill wont cause it) happens in drive and reverse but not neutral or park BUT if you are in drive and hold brake down and give it some gas it will occur.

The noise sounds like a combination of a bearing going bad / electronic type noise (kinda like your computer's hard drive when loading something)

The noise comes from the front left area of the drive belt about mid way down (facing the front of the vehicle).

I've seen some similar threads here and Alternator seems to be the culprit, replacing the pulley to be exact. But then you wonder how that pulley can make that noise... well it turns out it is a flywheel pulley which is a.... Sprag Clutch is a free-wheel device having an inner race, ... There are 3 basic applications for a sprag clutch: overrunning; indexing; backstopping. These pulleys can eventually slip in either direction making noises themselve or with the alternator bearings. But I've been told the noise isn't coming from the alternator so........ back to square one but still keeping this in mind.

Another theory is some sort of electronic clutch but the only ones I'm aware of is on the A/C Compressor and the Supercharger. Problem is the supercharger is to far left from the noise and a/c comp is way to the right. Also the s/c only kicks in at 2k rpm so why would its clutch be giving me issues around 900-1500? Now my A/C doesn't work which I'm aware of but im 95% positive it just needs freons charged. But both have electric clutches so........


I've had this noise for months now and it's embarrassing in parking lots yet its never gotten worse or caused a problem nor hampers anything other warning signs except the sound.

Welp!

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I had the same thing happen to my car.
When I was in gear at a low rpm my car would make a high pitch WOOOOO girl type noise. It baffled everyone i showed it to. Turns out it was the transmission. Somehow a small chunk of metal like a washer got into the transmission and flowed through the tranny fluid till it got grinded into a fine powder and was just tearing shit up. Had to get a new trans.

I'd have a mechanic check it out dude.
 
DewChugr said:
Get a mechanics stethoscope for about twenty bucks and you should be able to pinpoint the source.
Click to expand...

^This.

Unless the mechanic you already took it to tried it. If they didn't well - maybe take it somewhere else :)


The other alternative is to lick the battery terminals until you feel better.
 
Sounds like the 7th Fetzer valve is sticking. Maybe just lube it up with 10 quarts of Prestone AntiFreeze....no make that Quaker State and some 30 weight ball bearings.
 
I asked our car guru at the office (he said thanks for the pics). Below is his response.

Disclaimer: I have no idea if what he says will help or hurt.

It can be a number of things:
Bad, belt flywheel pulley, alternator, fan, water pump, ac compressor, and even drive shaft assembly. The only way to rule out stuff that has to do with the belts is (not something that a real mechanic would recommend) to first over tension the tensioner on belt so it applies access pressure on the pulley (if the belt is old it may fly off and damage stuff, but then it should be replaced anyway) and rest of the spinning components, and drive it for a mile and see if the noice goes away or changes to a grinding type of noice. If it does go away or changes into a metal to metal type of grind it is most likely it has to do with one of the spinning components being powered by the serpentine belt.
Procedure to determine which it is:
1. Loosen the tensioner.
2. Slip the belt over each of the spindles (with ought removing it) while moving the spindles up and down and side to side.
3. Once you fine the spindle that seems loose/broken or moves freely and does not spin easily then you know what you need to change.
4. If you do not find anything then I would look for something closer related to more internal stuff such as the clutch inside the compressor and even the driveshaft connections.

By spindle I mean the circular structure which connects the belt to other components and that if the belt is old (old=75k), he should just loosen the tensioner remove serpentine belt and check everything by hand and then when he finds the problem replace the part and the belt.
 
If you remove the belt and run the car a minute that might narrow it down. If it still makes the sound it's not the ac, water pump, alternator as they won't be driven any more.
 
edit- didn't read it all.

stethoscope that routes into your car with headphones is your best bet. (headphones so that you can listen while driving)
 
Take it to a transmission shop hopefully one with MB experience. MB Autos are kinda strange.
 
It's unlikely that it is any of the drive pulleys if it were the noise would continue if the vehicle were in neutral. From what your saying the noise only happens when the engine/trans is under load. It almost sounds like a water pump but again that would still make noise in neutral.

It is difficult to diagnose without hearing the noise. Here is what I would do first. Check ATF when vehicle is warm and sitting on level ground in neutral.

Check tension pulley/s they move slightly under load. Have you changed or worked on anything recently?

Have a buddy sit in the car in drive and hold the brake and get the engine under a slight load while you listen closely.

How loud is it? Intolerable or could it be a natural sound IE: supercharger whine Ect..

Just thinking out loud.
 
And also - I am fairly certain superchargers have no clutch at all. It doesn't turn off and on like a A/C compressor would. It is "on" when it is spinning enough to create pressure (boost).

If it is the S/C, it could have bad or scorn bearings that only rattle at a certain vibration.

Also- as stupid as it might sound, make sure it isn't a heat shield rattling.
 
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