mongoose2231

Hey all, I'm a newb to the forum. Done lots of searching everywhere to find an answer to my issue but I figured this would be my best bet. I've ran some searches on here and found this https://mbworld.org/forums/c32-amg-c...ngine-bay.html but it happens to people only when the car is running. I parked the car yesterday and it made this really loud "kind of like a drill" sound from under hood on the right hand side somewhere. I was wondering what it was. Car functions as it should. It's an 04 c240 4matic wagon. Great little car with 140k on the clock. Just wondering if you guys know what it is so i can just replace the bad part. Again it did the noise yesterday only for the first time after engine shut off. It was def not the fan. Any help is appreciated.

mongoose2231

Does anyone know what this is about? I am thinking it cannot be any of the car's regular systems as the engine is off. Def not the fan. Noise was horribly loud. Almost the decibels of a car alarm

RWDlifer

I have a 230k and I normally hear a weird mix of humming and clicking during starts (before starter is engaged) and sometimes relay clicks after shut down. I can't imagine what your car is doing, but my guess is it is something electronic rather than mechanical, since it happened with the motor shut off. This is a far flung idea, but try seeing if there are any pending codes, in my experience some faults may be stored that do not quite meet the requirements of a CEL.

mongoose2231

Thanks for the reply. I will try to replicate, but for now it looks like all functions normally. We'll see and post after findings.

VVF

Sounds like your alternator freewheel pulley might have seized.
As you turn off the engine, the V-belt stops, but the alternator keeps rotating - hence the sound.

How long is the duration of that sound? Do you have time to get to the engine bay and look at the alternator?
Or have someone shut the car down while you are looking in the engine bay.

RWDlifer

Hmmm....your statement is contradictory...if the pulley is seized, it will not freewheel..
The alternator is designed with a freewheeling pulley.

VVF

I thought the seized pulley may keep spinning against the stopped belt making the sound.
Or maybe it's partially seized, and the internals of the pulley itself are whining...

RWDlifer

The op states the noise is present after shut down..that pulley would need a lot of kinetic energy to continue spinning by itself on a stopped engine.
I just had an issue with an alternator pulley a while back, generally when they seize they generate a noise on startup and it's the other pulleys that suffer, eg compressor...
Doesn't the 240 have that weird electronic intake manifold with lots of electric bits and pieces? OP, if possible, when you get home, leave the car running, pop the hood and have someone else shut if off while you listen. It may take several tries, but you would have a better idea what's causing the noise. Sounds generally bounce around in the engine bay and can be difficult to pin point, esp with the hood closed...

mongoose2231

Allright everyone, thanks for all your replies. I just replaced the alt a couple hundreds of miles ago as it was giving up the ghost. Everything is tidy under the hood. The belts and all the devices run by the belt are properly functioning. This sound that happened last Sunday was very simillar to the sound of a power tool. Kind of like a big drill. Very loud. It required me to really raise my voice for my wife to hear me when I told her to pop the hood. The sound was definitely coming from somewhere under the passenger side fender lining in the front. Car was completly off for at least a few minutes before it started. First time lasted for maybe 20 seconds. Then stopped for like 5 then it went on for another 10 seconds or so. It's really weird cause we have been driving the car since and has not happened anymore. I have no idea what could still be running after minutes aftetr shut off. I though someone migh have encountered a simillar issue.

BigN8

Did you have the hood open when it happened?

The cooling fan can stay on after shutdown. That could have bad bearings/motor that made the sound.

mongoose2231

I never had a chance to open the hood but it was definitely on the rigth side of the car. The fans work fine. We drove tha car last night. I am inclined to belive that there may be an electrical module or a pump of some sorts under the fender liner there, that might have just experienced a bad day....I dont know what to look at. I do most of my mechanical work and I'm confortable fixing things but this just puzzles me. The car functions just fine now, a week later almost. I have to mention that the car is driven very sporadically, perhaps 20 miles every weekend or so. It's my wifes car and she doesn't drive much.

Poptrunk22

I had a similar noise on my BMW recently. Start your car and pull the oil cap off and see if it goes away.. it probably will be hard to pull the cap but do it anyway.. if it goes away then you have bad ccv valves and need to replace them