W203 C270cdi noise after turning off ignition

[renrutp76]

for a couple of months, my C270CDI made a loud noise after turning off the ignition. The noise is difficult to describe, the only thing I can say is that it lasted for a couple of seconds, and got gradually quieter. Now the noise is barely noticeable, but I have traced it to a small filter at the front of the car (behind the drivers headlamp). is thus part of the vacuum system? I may be getting paranoid but the brakes aren't particularly sharp, however the headlamp auto adjust works when the car is started.

any help would be appreciated

 

[thejohn]

I'm no help but mine makes the same noise and has since I brought it in Jan. I thought it was normal so i'm interested in any feedback.

 

[renrutp76]

Replaced waterpump and alternator pulley, noise dissapeared:lol:

 

[Rory]

That's a bit worrying - mine makes what seems like the same noise and I also thought it was coming from the vacuum system. Was very noticeable under the bonnet the toher day - almost like a fizzing noise.

 

[Wirral_guy]

If it's the same as mine, a cross between a fizz and a buzzing noise, my 270 has always done it.

Dave

 

[johncroydon]

mine makes a buzzing noise for a few seconds, like above i thought it was normal

 

[Alex Crow]

The vacuum buzzing is normal and correct, and is just the metal plate in the bottom of the modulator (or rather both modulators - EGR and turbo) buzzing as the vacuum drops.

However, in this case it seems it was the alternator pulley.

 

[Rory]

However, in this case it seems it was the alternator pulley.

I'm baffledhow the waterpump and alternator pulley could be noisy after the ignition is turned off - unless the OP means as the engine is coming to a stop, but that strikes me as unlikely.

 

[Alex Crow]

The OAP (overrunning alternator pulley) can make a noise after the engine has stopped, as the alternator slows down.

renrutp76 said in post #3 above that the noise complaint in this particular case stopped after replacing the water pump and alternator pulley.
If we take this as correct, it leaves few other conclusions.

Possibly when looking for one noise (maybe heard very briefly after the engine had stopped) more closely, another was found (the vacuum buzz).
We often see customers present with noise complaints, that have confused one for another - easily done.

I am sure renrutp76 still has the vacuum buzz, if not I would guess a vacuum pipe was knocked off while changing the other parts.

 

[renrutp76]

Thanks Alex,

The vacuum noise is still there and I am told is quite normal, however there was also a screeching noise at the same time, cured by the replacement on the idler pulley, and the water pump.

Apologies for not explaining myself very well:Oops:

 

[Alex Crow]

Thanks Alex,

The vacuum noise is still there and I am told is quite normal....

Yes, that was me last month

Thanks for confirming the facts and glad you have it fixed now.