jmcar1

I have a 2011 4matic with 700 miles on it. This is my 3rd mercedes but first 4matic. When I'm driving on the freeway, say cruising between 65-80 mph, I seem to hear and feel this strange rhythmatic rumbling/vibration type noise. It's almost like a humm...123....humm...123..etc. (the humm being the noise and the 123 is the interval between the noise). I notice this mostly on good highway roads. Not so much if the highway is not good. It's not a loud noise but I do hear it and feel it in the steering wheel. It does not happen at slower speeds. Is this an AWD drive issue? I'm trying to get used to the 4matic characteristics and such and this does not seem normal to me. Time for a visit to dealer?

ttoE550

There is very little difference in feel between an AWD car (had many) and any other car while cruising at highway speeds. The only real difference I feel at all is a bit of torque steer and more acceleration grip in snow and rain.

Do you have lane control assist? The hum could be the rumble strips on the road, and the 1-2-3 (I call it "snick-snick-snick") could be your lane control assist -- both would tend to sound about the same time.

EDIT -- reread your post -- to be clearer it's snick-snick-snick then pause 1-2-3 then snick-snick-snick. It's a sound and a vibration sent through the steering wheel.

hyperion667

hmmmm.........weird, I've never noticed any strange sounds as you descibe, and I'm a sound freak man! good luck and ket us know how it goes........

ImInPA

It is very likely the tires. Modern tires have very precise and sophisticated tread designs designed to minimize tread noises. Since there is no way for a tire manufacturer to test their tires on every possible surface, there are always roads out there that can cause these undesirable harmonics. I find the run flats on my Bluetec are actually pretty good on most surfaces, but, there is one type of new black macadam in my area that is really noisy and most concrete expanses are pretty noisy. As the tread wears, these harmonics can change.

telemakhos

I hear/feel the same thing with my E350 4Matic on the highway at those speeds. The interesting thing is that I heard/felt the same thing with my 97 E320 (rwd). I got used to it on the old car and it was pretty minor so I never did anything about it. I didn't think that bringing this up with the dealer was going to get anywhere. Now that you brought this up, I may check with my independent mechanic.

petee1997

This is proof that these cars are made for older people. My car is extremely quiet and as I get older and my hearing fades I find that every new model is better than the last.

CEB

Right. In addition, rft's tend to be a bit noisier as they have stiffer sidewalls.

mafialink

Interesting. I am getting mine next week. (4matic) The only reason why I am getting the 4matic is because it was cheaper. (strange huh!! I guess they wanted to get rid of it) In any case I have in FL so dont think I will ever take advatage of it.

So this poses another question.... From a perforance standpoint, is there anything different in the 4matic then without. Other then weather ofcorse.

ttoE550

Depends. If I remember right, MB says about .1 or .2 second slower in 0-60. Probably a little more weight. Some say it is faster when traction control is off because of more grip off the line.

Unless you are drag racing it, it's probably something you'll never notice. Until you shoot off like a rocket on a wet road...

jmcar1

Thanks for feedback gents. Another mercedes owner here at work indicated that my "harmonic hum" might be the rear differential. But I doubt it with only 700 miles on the car. I might just swing by the dealer and get their input also. Doubt if they will find/do anything however.

Arrie

It sounds like an issue with two vibration sources with almost the same frequency. Almost every airplane with two engines, especially prop planes, have this same issue. You can hear and sometimes feel vibration that gets louder and quiets down just like you explained.
I don't know the correct word for it but this condition is caused by two almost equal vibration sources multiplying and canceling out each other in an internal. It happens because the vibration amplitudes are added together and when the waves are in the same phase you hear it the laudest. When phases from the two sources are opposite they cancel each other out.

In a car the vibration sources are the wheels and not so much the tires I think. Thread pattern between two similar tires is so close the same I don't think there can be any difference in frequency they produce against road but I could be wrong with this.

Vibration sound going up and down requires two slightly different vibration frequencies. This would be two wheels rotating slightly different speed, which would mean tires are with slightly different diameters.

You can try to observe how it acts during drive thru a shallow curve on a highway. It should change the interval of the vibration.

ghh429

You'll lose a bit on fuel economy and performance on the 4matic. There's the drivetrain loss + the extra weight. Neverthless certainly I would get a 4matic if it was cheaper.

telemakhos

The term you are looking for is "beat frequency".