I have a 2005 300C with 64,000 miles on it. I love this car!
Recently when I accelerate from stationary to 40kmor even when accelerating slowlyon the highway.... I noticed a humming noise coming from the car.You can no longer hear the noiseonce I go past 100km/h. The most recent work done on the car was replacing an EGR component and the air filter. I don't hear the noise when decelerating. One of my friend said it might be the transmission.. another said it might be the air filter not fitted properly. I brought it to the dealer and they said you will need to have to service the tranmission(changing the transmission fluid) which I did at 30,000miles.
Does anyone have this problem or have any solutions?

 

Did u solved the problem?

I have the same problem on 2005 c, 48k.

 

Can u first tell me if this sound comes out only while AC is working or not cuz I used to have a similar problem!
If so u need 2 check the AC compressor, but mine was more like a squeeqing noise and when I replaced the compressor the noise disappeared !

 

Probably the flux capacitor warming up. I've not noticed this on my "C", but she has only 29K. The rumble would probably drown it out anyway.