Turns out, the plastic in the grille warped slightly and was causing the noise. I am so happy to be rid of that noise. It was super annoying.

Bought my car December of 2016. 2014 w204 C63 Base Model with only 2500 miles. Didnt take long for all the rattles and whistles to start annoying me. I deal with this kind of stuff on almost every car ive purchased. My job is to pick out nuances in operation to prevent failure so that trait carrys unfortunately... One noise in particular had been elusive to two dealerships and a few technicians. Didnt matter windows up/down, HVAC on/off, recirc on off....between 47 and 53mph there was a dog whistle in my car. It was so faint and intermittent, but i was fully tuned into it. It would stop with Rain. Rarely I would hear it over the radio....but then i just put on some Rick Ross and that would get rid of it. Needless to say, that had gotten really tiresome. I tried taping up all the window seams to try and help out technicians on the car but no dice. Removed those stupid plastichrome fingernail guards on both doors...turns out it was the platichrome on the front grille.

Plenty of noises in this car...the passenger seat belts whistle with windows open and a strong cross breeze. The rattling rear decklid is an ongoing issue, already been replaced twice. Also, I dont like how the engine whines like my 88 mustang PS pump. Im told its the 4 cam setup...I dont like it at all.

Oh ya, How about that engine rattle on startup?!?! WTF is up with that design flaw...im sure thats a beaten horse on this forum lol...

It is time to make this car louder now that the dog whistle is gone. Remus Cat back is tucked away in the spare bedroom...didnt want to hear the "We cant hear it with the aftermarket exhaust" BS...luckily i found a great dealership on Long Island. Totally changing my negative ownership experience into a positive one.
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It annoys me, my seatbelts don't whistle but they flap around everywhere even though they sit firmly against the rear seats (passenger front also flaps around). Have never had this issue in other cars but it is annoying when I have all the windows down.

 

Perhaps the seatbelts is a non issue in the sedans?

 

Mine is sedan :/

 

 

 

Ill be sure to tell my tech when i drop it off...love me some warranty!

 

I had the dealer check mine out a couple of years ago and they reported the Xentry showed normal. The temp. coming out of vents was considered normal.
Mine was blowing too much cold air out of top vents at certain times. Someone said probably one of the multiple sensors.
So, I just use the little wheels on vents and close down the vent until the air matches what I want.