Cartertime

Hi, I'm new to the Forum. Last month got a 2010 C300 for my wife and after about 500 miles she tells me she hears a whine-sound (kinda like a fire engine at low volume) coming from the front of the car as she decelerates. Sure enough, I drive yesterday and hear a 2-part "wind down" sound as the speed/RPM's decrease (ie, volume up, volume down then up and down again). We take to service and tech tell us it's normal. So we drove 2 new cars (pretending to be buyers) and neither of us hear the noise. Any clues as to what the noise is? Thank you.

mbx84

had same problem,have no idea how to fix it

Sportstick

Does it relate to road speed or engine speed? For example, if you rev in neutral, does the sound persist? Or, is it only while engaged in gear?

Certainly, if one of the quiet comparison cars is at the same dealer as doing your service, get the Service Manager to drive both back to back.

Cartertime

Just tested and this does NOT seem to happen after rev'ing in neutral. Does that help with a diagnosis?

Sportstick

Not positively, by remote control! But, probably not a drive belt. Next, try getting up to a normal speed and coasting down in Neutral, when you would normally expect to hear it.

Cartertime

Thanks for replying. Question: Do you know yours started from day 1 or after you put some miles on the car? I'm wondering if that's why we're not hearing it in the brand new cars on the lot.

Sportstick

At 11,000 miles, I have never had this sound.

AMGTTV8

Try turning the "a/c" off when driving with the air on...this gets rid of the problem for me, but leaves me really hot - not much of a solution, I know...

Leaving just the fan on seems to get rid of the problem....sometimes it does take a minute for the noise to disengage

akbro93704

My car makes this "whine" when coasting down from freeway speeds...probably from about 80-65. Haven't heard it otherwise. Mercedes V6's (at least the newest DOHC family) do have an inherent "whininess" at lower RPMs though. Maybe you're hearing the engine RPM's fluctuate as the transmission downshifts when slowing down.

Blazeitup123

i have this sound in my GLK350.

Cartertime

Thanks for the replies. So if this noise is a result of engine RPM's fluctuating as the transmission downshifts, is it safe to assume that it's simply louder in some cars than others....and that's why we couldn't hear it in other C300's we drove? Is there some way to "insulate" the noise so we can't hear it in the cabin of the car? The radio has to be on awfully loud to camouflage the sound.

Sportstick

Hmmmm.....I thought we might have ruled that out by not having the noise during standstill revving. Did you do the neutral coastdown test? (Find a smooth straight road, speed up to around 60, if the speed limit allows, place in N, and listen while you coast down.) If you hear the sound with the engine at idle and with decreasing road speed, the search will be elsewhere than the engine.

If you 1) don't hear it at standstill revving, and 2) don't hear it at neutral coastdown, but 3) then do hear it with a coastdown in gear (normal driving) then some other part of the powertrain becomes suspect.....I think.

Cartertime

Just did the rev test again and I was wrong before. I DO hear it loud and clear at standstill revving. To my untrained ear, it sounds like I'm hearing (but shouldn't be hearing) the "noise" of the engine winding down...and that noise happens to sound like an emergency siren. Tonight I will do the neutral coastdown test and report back. Thanks again for trying to help us. I'd like to come armed with info before the dealer tells me it's normal.

Sportstick

That would suggest bringing the focus back to the engine, belt, water pump, steering pump, a/c compressor, etc. anything related directly to engine speed and tends to rule out anything downstream of the engine, such as driveline components, related to road speed.

If you get pushback, be sure to go for a ride again with the Service Manager in one of the other new vehicles you experienced which were quiet. The next argument to anticipate is that this sound is "within normal tolerances". That is your cue to request a meeting with the MB Technical Specialist at his next visit to that dealership, with an eye to mandating repair, once the root cause is found, or a vehicle swap. Your position should be that the test drive car before your purchase was quiet and you made your purchase with that expectation. Emphasize that point so he records it in his contact notes with you.

dcjwlee

I have noticed this in all V-6 Mercedes that I have driven, the E320 Sedan, C300 Sport 4matic Sedan, and the new E350 4matic Coupe.


I notice the sound most when I let the car coast to a crawl from around 40 mph on the private road approaching my house. The reason being this is where I tend to turn off everything in the car -- audio, a/c, sunroof, heated seats etc...

I personally like the noise, it sounds like a fighter jet on approach for landing lol. Methinks it fluctuates with rpm not road speed.

The V8 I drove in the 2006 MY ML light truck was nicer though, the thing shook the room above the garage on start-up and idle and at WOT had this whirring 'roar' behind it that I miss so much.

Cartertime

You guys are terrific! I know so little about cars but I do know about the "it's within normal tolerance" line. Sadly, I'm anticipating that to be the answer...and I'm also prepared to take it to the next level if that's the case. Thanks for the tip that my position needs to be that the car(S) that we test drove before our purchase were quiet and accordingly we made ourpurchase with that expectation.

I enjoyed the last post because even though my wife is really bothered by the noise I told her that I thought it was pretty cool sounding (love the jet analogy). And, yes, it is most audible coasting to a crawl from just about any speed. But now that I'm listening, I'm hearing the noise (though a little less obvious, but not by much) on acceleration as well. You too?

Keep the tips coming. Much appreciated. She is very unhappy. We're meeting with the shop foreman later this week.

Sportstick

If you have a meeting arranged, tell them you plan to leave the car with them at that time and request a loaner. If they resist, ask them who at MB's national owner relations you should contact. Obviously, you can make the call on your own, but this lets them know your plan. And, do make the call prior to the meeting to let MB know what's happening and that you expect alternate transportation while they figure out the problem. Part of the strategy here is to get the car back in their custody with low mileage.

And, I've never heard this sound on either of our cars.

AMGTTV8

has anyone tried isolating the noise based on my recommendation of switching the A/C button off??

Just curious - I think a few of you will find this to be the culprit...start your car with all a/c and air off...you should hear silence when driving at all rpms and speeds

Cartertime

A/C in "off" position, always. I can't imagine there is any connection.

WARVET78

I got that problem in my 08 and it's the power steering pump!!

AMGTTV8

Trust, this is what I have to do to make it disappear - so imagine. LOL

Sportstick

Those of you who drive around with A/C off may want to reconsider. Check the thread about bad smells from the HVAC. It may not be absolutely conclusive, but the folks who leave it on AUTO (and can adjust the fan if necessary) seem not to have the mildew smell complaints.