GateKeeper

not lost in mine, it works

Canadian model

I turn off the car to conserve fuel while waiting for my wife, I hit the button, and the warm air keeps on flowing, it's nice now that the winter months are upon us...

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Merc_F1

curious, any solution or cause for this weird intermittent buzzing sound

C300Sport

I have only had it happen again once over the last several months so I am not too concerned with it anymore...seems like all is well.

jmar

My car is now doing this exact same thing, and to boot the battery is no dying (coincidense?) I first noticed the sound after washing th car 2 weeks ago, but today it began again, and I didnt washer her today. Weather was about 80 most of the day, and I did run the A/C while driving. Anyone ever have this issue diagnosed? My car I's a 10' C350

RLE

You have answered a 2009 post, you do realize.

Your description of the noise is a bit vague but if you are referring to an intermittent high pitched squeal/whistle, it's AC refrigerant moving through the system equalizing pressures after shutdown and is entirely normal. My 2008 still does this at times after 4.5 years.

C300Sport

I don't know if that is so bad...I would have to give him props for actually searching the threads!
I have used a stethescope to check the noise since my last post on this and it is coming from the brake calipers. I can only assume it is the drying feature being active for whatever reason. It doesn't happen often but when it does, it will do it anytime the wheels are rinsed but not once they dry out a bit.
It makes me think the drying feature stays active sometimes when it should be off???

jmar

Yes, I am aware of the post being originated in 09' what's your point? My car is doing this now, and there was never any closure as to what was causing this similar occurrence on other people's vehicles, therefor I figured I would ask to see if anyone out there over the years has ever definitively discovered the cause, hope this is ok with you?? C300, sounds like your write up is most similar to what I have experienced ,but my issue would last for hours and this last time I hadn't washed my car, nor was it raining. The sound is best described as being that of an electric motor/air compressor Turing on for a short 1-2 sec. Burst, every minute or two. Drives me nuts not knowing what the he'll it is. Definitely not no refrigerant running thru the system as described. If seems to be coming from the left front wheel area, but but not determine exactly where specifically..... Thanks for the input guys!

C300Sport

Jmar,
Did you say that the battery is now dying?
Does the car make the noise all the time or intermittently?
If the battery is dying, is it only when it is makeing the noise?

jmar

Intermittently, I've only noticed it twice so far over a 3 week period. My battery was somewhat beat up from me listening to tuple radio with the car off over a one month period. But I charged it and it was fine until a couple of days ago. I went to my cousins house for a BBQ for about 2 hours or so and when I went to leave my car didn't have enough juice to crank over, and I noticed that damn sound when I popes the hood. Don't know if one thing has to do with the other, but it seems to be. As you mentioned the sound appears to come from the left front wheel area. Drives me nuts not knowing what it is.....

acr2001

FYI, while these cars do not have REST in the US the fan still DOES come on after you get out of the car. This is built into the system in order to help remove humidity from the system after using the AC and prevent mold buildup - a very nasty problem that MB just can't seem to properly prevent in a large percentage of vehicles. I would guess this is what you guys are hearing. I'm sure there is a technical paper somewhere that states under what circumstances the fan comes on.

RLE

Perhaps you could describe your understanding of how this function works?

C300Sport

The concept is pretty straightforward but I do not know much about how Mercedes has developed and built their system. I suppose I could Google it or perhaps you could enlighten us all on exactly how the function is supposed to work and help progress everyone’s understanding?
I will just clearly restate that I am making an "assumption" that this could be a possible cause. As the noise is not coming from the engine bay, the wheels/tires, suspension components or anything that is not within a few inches of the brake caliper, I thought it to be a reasonable possibility but am certainly open to other ideas.

MBRedux

Did you briefly move the car to the spot to wash it first? Then as you started to wash the car, you heard what sounded like a low servo motor perhaps? Hmmmm? Wish to know what it is?

acr2001

It's not the 'brake drying function'!!! That feature works by bringing the pads closer to the rotors and shedding water. You would never hear it without the car running because it simply doesn't work that way.

C300Sport

Well, the lights are not supposed to come on without me doing anything to the car as well....but they do...and then often don't work when they are suposed to be on. Once I get the defective switch replaced at my next service, I hope they don't do it again. I was told categorically that this was impossible until I showed them a video clip of it happening.
These cars are pretty complicated and I know enough to never say never because sometimes a car can leave you wondering how and why it does some things.
I am not sure if this sound is normal, abnormal or just plain weird, but it happens and the noise is from the immediate area of the brake calipers

C300Sport

I have done both.
When I parked under a carport, it could be a day or more since the last drive and it would do it. Now that she is in a garage, I usually start her up to back up though I have slipped her out of gear and just gave a little push back to get out the door.
It seems to happen about 10%-20% of the time. I didn't think much more about it after the first round of comments on this thread. Late last year I borrowed my neighbors stethescope and camera system to track down something then pulled it out to search for this sound after hearing during a wash.
The sound does sound like a servo motor engaging/disengaging.

acr2001

Sorry, I thought we were all discussing things the car does "within normal limits" - when there are no errors or bugs presenting themselves. Since multiple members posted mentioning that the car will make this sort of noise. Naturally with faulty electronics all sorts of things could happen. Still, I believe that there is no servo or motor in that area that functions as part of the brake drying function.

RLE

There is a Mercedes document someplace which describes what activates the drying feature which I have read. The obvious question is how the system knows when the brake discs will be wet. Well, since the discs are wet when driving in the rain, the wipers are on and that is what activates it.

C300Sport

Thanks for the info. After reading about the system yesterday, I now wonder if an anomally in the wiper system could have something to do with the noise? While washing/rinsing I do keep the entire car wet prior to drying to prevent spots so maybe it's not the wheel area being wet but the rain sensor?
Obviously, I don't know exactly what's going on but just throwing things our there to see what sticks.
BTW: I spend a decent amount of time at and around my work bench within 10 feet of the front of the car and have never heard the noise when dry.

RLE

I'm sure nothing works without the ignition on. And, the description I read did not mention the rain sensor.