My 1994 E320 has a harmonic sound that seems to be coming from the rear end. It is not a whine but a harmonic sound. The sound is noticable at 35 mph and faster until road noise disguises the sound at higher speed. I had my wheels spun on the car to rule out wheel bearings. My mechanic says it is not the differential because differentials whine. Has anyone experienced anything like this?
Thanks!
reubengeg

is the sound constant, repetitive, or variable? Does it change with wheel speed, engine rpm, or is it independent of those?

The sound is constant. It does not increase with rpm.

Is it like a "singing" noise that keeps the same pitch but varies in volume? That could be a lot of things coming together at just the right time, culminating in a very annoying but probably harmless sound. I would guess that a lot of it has to do with the particular tires that are on it. Are the front and rear tires the same?

Yes, the sound is like a hum or singing. The pitch is the same no matter the rpm. As I said, I had the tires spun on the car at Gran Tourismo, one tf the best tire shops in Atlanta. They did not detect any problem with the wheel bearings as they spun and balanced each tire. The tires were Goodyear Assurance 16" that I swapped off od my 190E. The tires had about 9,500 miles. I replaced the tires with brand new Michelin's and still have the same sound. The car has 48,000 miles original miles. I also had the differential oil flushed and replaced. I do know that the car went off the road before I bought it as the exhaust system is bent. However, there is good clearance and nothing rubs. Drive shaft appears to be in good shape, cv boots are good with no signs of creaks or tears. It may be a harmless sound but it is bugging me to death. One cure is to play the radio but I'm on a mission. Any ideas will be helpful.
Reubengeg

lately I've noticed that my car is starting to hum from the rear a tad...it's not to the point where it's driving me insane, but I can def tell that it's rubbing somehow.

I think I have camber issues and the 225/55's in the rear may be starting to rub inside the inner fender.

I'm not saying this your problem but it might give you some ideas. I used to drive a Chevy Astro with an aluminum extension ladder on top. It sounded exactly like you are describing as the wind exited the metal rungs of the ladder like a reed on a saxophone. Maybe the bent exhaust is doing something weird?

I had a roof rack on a previous car that did the same thing. The crossbars would hum like crazy until I put a fairing on it.

Another guess: If possible, have someone press on each window while driving to rule out the possibiliy you have a very small leak through a seal. I had that problem in the windshield of my Ranger pickup.....that was a royal PITA but easily fixed once found.

I would bet money that it is a hole in your exhaust system. Somewhere. It sounds like a constant hissing. I had a crack in my oem muffler and 2 in my resonator and it did the exact same thing until I got the system fixed.

Lets make certain that he doesnt mistake the fuel pumps for an exhaust leak.

I think the service manual lists a common problem of noise due to a body panel problem near the rear wheels. I'll look it up once I get to work.

cool thread title

OK, I checked the service manual and the noise I was thinking of was a problem with the window guide rail for the rear window making a wind noise. The problem was corrected at the factory as of 3/87, but the change they show in the design is minor. I don't think this is specifically what your problem is, but it just goes to show that something minor can cause a loud noise at speed.

Uhmm...didn't I already say this?

Do you have an external antenna for a phone on your window?

I bought a new 400E in 1992 and I had the same exact problem - it was the cellular phone antenna which was attached to the back window (I know - it was 1992 - old school) I put a tube through the coils of the antenna and taped each end - broke up the wind and stopped the noise.

Here is a pic taken in 1999 - Midnight blue - beautiful car - had 100k miles in 1999 - sold it about a month after this picture for $21,000.00.

Yes, I was confirming your idea.

Guys, Thanks for all the ideas. I've been out of town the last few days so I haven't been able to respond. There is something new that I discovered today driving back from the airport. When I drive in a straight line I hear the humming noise. When I steer aroubd a turn to the right I hear it. However, If I steer to the left around a sharp turn the sound disappears. Could it be that one of the wheel bearings is bad?/ I thought that was ruled out when my tires were spin balanced on the car but perhaps it takes weight on the axle to cause the noise. So if turning left eliminates the sound which wheel bearing would be the most likely cuprit? The left one or the right?
If this is not the problem I suppose I could use the car exclusively to go around our cul de sac. Anyone wants to take an educated quess?
Thanks again!
Reubengeg

Well, it definitely sounds like a wheel bearing. I'm guessing the right bearing because a hard right unweights the right rear wheel.

Does anyone have instructions on how to replace rear wheel bearings?
reubengeg

I think you need a press. The front are DIY, but you need special tools for the rear. Anyone else know for sure?

I had my mechanic and his partner ride in the car with a stetoscope in the back seat and he decided it was the output shaft of the transmission. He said leave it unless it gets louder, it has been the same low whine for a couple of years. He ruled out the wheel bearings for some other reason. He said if it gets worse to start saving money for a new transmission but not to worry as most likely it will never get worse.
Kurt
1993 300CE

I dropped my harmonic E320 off at a local MB repair facility last night for a diagnosis. This is a great shop near my home in Duluth, GA. They called me mid morning and said that the sound is definitely the left rear wheel bearing. The mechanic also noticed that the sound was no longer audible when making a left turn. Once on the rack with engine running they used a stethiscope and pinpointed the left rear wheel bearing. The repair is difficult, ie, 4 hours labor plus expensive part. All total the estimate is between $500 to $600 to replace the bearing. I am happy to pay the price as this is no DYI job. I should pick up my car in a day or two and will be extremely excited to get past this anoying problem. My car only has 48,800 miles. It's hard to imaging why a wheel bearing would fail with such low miles. In any event, thanks to all for the excellent ideas and suggestions.
Now! I can truly listen to Phil Collins and enjoy the sound!
reubengeg

I had this same hum noise on my rear passanger side and when they lifted the car the wheels was loose and my wheel bearing was gone. It was done in a day and cost was $150 for the it. You need a special puller to take it out but i don't know why it's $500-$600 to replace it. Are they charging $90/hour?

If i wanted a new hub and bearing it would be $110 for the new hub and the $150 for the bearing. Are they chaning the hub too?

If you do a search on mbworld you'll see that i had this same problem...

Yes, labor is $80 per hour. They said 4 to 5 hours labor to replace the wheel bearing plus cost of the part. It may be bit high but anytime I have used this shop I have always received quality work and never had to bring back. I know them and they know me by first name. I find value in that. Anytime I have a question I can call and talk to the owner and get a straight answer. I find value in that. Most things I repair myself. But as dirty Harry once said, "a man has to know his limitations".
reubengeg