I posted this some time ago. My 03 E500 has been making some strange noises at high way speeds. If I take the car up to 100 really quickly and then start slowing down gradually, I hear this noise coming from the rear. It sounds a bit like a piston slapping noise, but obviously its from the back so its something else. It gets faster and higher pitched as I go faster. Once the sound starts, it continues prety much the entire drive until I get down to speeds below 40. I've also noticed it popping up on long highway trips.

I took the car to the dealer and they replaced the entire rear differential..yet no luck. Any suggestions on what I could try next? I thought it might be the tires, but I had them rotated and it still comes only from the rear. It doesnt sound like road noise but rather something mechanical. i also notice a slight vibration in the gas pedal.

 

I am no expert but since you and I have the same car. I will take a stab at it. You know our car will lower about inch when it reaches certain speed, especially at highway cruising speed. It will rise to the normal height when you slow down. Maybe, just maybe, the problem is with the airmatic suspension. Ask the dealer to check it out.

 

Could it be the siren of a state trooper???

 

hmm dont think its that. the sound goes away randomly sometimes on its own and raising/lowering the car has no effect. It sounds like its coming from the drivers side, but im not 100% sure. Can it be the wheel bearings?

 

i replaced all 4 tires and got everything rebalanced and im still hearing this noise. I've noticed there is no change if I put the car into neutral or if I switch gears...it seems the sound is completely dependant on the actual speed of the car. It usually starts around 60mph, however if I'm driving normally it doesnt actually become noticeable until 5-10 min into the drive. However, if I speed up really fast to 100 and then drop back down to 40-60mph, it comes up right away. I've also noticed a vibration in the steering wheel which gets worse as I speed up. At speeds of 100+ the vibration in the wheel and car is prety bad. Even at 60+ I can see the passenger seat vibrating. The pitch of the sound also gets higher as I increase speed. The best way to describe it is very fast ocillating propeller noise. Im gona take it to the dealer again, but any ideas on what I should have them check/replace?

 

Sounds like something is catching the wind and flapping around. Check around the door areas.

 

its defintely coming from underneath the car towards the rear. It sounds more mechanical. I think its caused by heat since it happens only after driving for awhile or from accelerating very fast. This is really bumming me out

 

I don't think it is the bearings. They would have been cooked by now. Your problem also reflects the modern day so called mechanics. They are parts replacers; they don't know how to diagnose problems. It is almost universal regardless of dealers or make of cars!

 

The problem could be one or more of several:

-An out of spec driveshaft (a friend of mine had this on the right side of his car)

-An improper centering of the wheel hub due to improper mounting, damaging the wheel and or wheel hub

-Wheel bearing

 

thanks for the tips. Can you elaborate on the out of spec driveshaft? How can it be on the right of the car when the shaft is in the center?

I think I can rule out the wheels completely. Ive had them rotated, and all the tires replaced & rebalanced and the sound still comes from the rear.

 

Why don't you go to the dealer and get shop forman in the car and go on the freeway and let him hear the noise.
It is there problem and let them deal with that.
All you have to do is to dublicate the problem in front of them so they can;t say problem can not be verifed (saw too many of these on my work order).

 

I wish it was that easy. I alraedy had them drive with me the first time and they confirmed the noise. THe problem is, you need to be driving for at least 10-15 min before it starts OR you need to speed up really fast to 100mph and then slow down. After they attempt to fix the problem , they are unwilling to go for such a long drive themsevels to make sure the problem is fixed. They are also unwilling to speed up that fast since ultimately it is against the speed limit. Also, I dont want to keep wasting my time going back in the shop and replacing new parts until its fixed. I wish there was another place i could take the car, but theres no other dealer nearby.

 

I don't know what is exactly meant by out of spec. Apparently it could either be coming from the center drive shaft (cardan shaft), or from one of the axle drive shafts for the right or left rear wheel (propshaft).

 

Have you looked under the rear (Left and Right) at the heat shields that protect the exhaust from burning your rear quarter panels. They are located right about where the tailpipe ends, they are somewhat flexiable and do have a tendecy to flap around against the tailpipe if not bent all the way back.

 

i did check under the car for any obvious problems. I dont think tis something that simple...I doutb the flaps would cause such a strong vibration in the entire car when driving.

Since the vibration and sound dont occur 100% of the time, is it safe to assume that the problem is not caused by any faulty driveshaft or axle? It sounds like something metal hitting another metal object really fast constantly. its relatively high pitched and the pitch also changes depending on the speed of the car.

 

The brakes? maybe. and also check the airmatic.

 

I was driving today, and I noticed that the sound also comes up really quickly if you corner a curve above 50mph. Also, Ive noticed taht the sound switches side when cornering...its typically on the drivers side, however if I corner on a left curve, the sound will switch to the right side (and then return to the left once back on straight road)

 

Also check your muffler hangers. I've never experienced it in an MB, but most of what you describe are the classic symptoms of this problem. It's usually a broken hanger, but could be a poorly installed one that's causing the exhaust pipes and/or muffler to hang wrong. If you have a broken hanger, then the muffler and/or pipes knock against the underbody when the engine torques one way or the other (as would happen in one direction when you jump on the gas, and in the other direction when you step off the gas after high speed -- in that case the engine will be twisted in one direction as it acts as a brake). Similar idea when you go around turns. Might also have the engine mounts checked -- again, some flaw/problem there may be causing misalignment of the muffler or pipes in the back.

 

I have noticed that the left pipe hangs lower than the right...ill have the dealer check this out. thanks

 

What you are describing is now indicative of a bad rear wheel bearing. It sounds like a textbook case of the early stages of bearing failure.

The reasons why I think this is: If the noise does not happen all the time, but rather after the bearing heats up, that means that they are still OK at the beginning, but are deteriorating. This is not safe!

The most important thing that you described is that turning causes the noise to start or to alternate. What this means is that there is definitely a flaw on a rear wheel bearing and it will only get worse.

You should try the following. After driving for a while and the bearings are hot/warm. (Also, the more weight you have in the rear the better, like a full tank of gas or rear passengers). Drive straight ahead at whatever rate of speed is the threshold for the noise to appear. Then, if the noise is intermittent when you start zigzagging, you will be able to even know which side is the problem.

If the noise appears, or gets worse, when you veer left; then your rear right wheel bearing is damaged. This would be double confirmed if the noise goes away when you veer back to the right. This action is actually shifting weight from one rear wheel to the other while at the same time adding weight to one side or the other. This is a proven way to trouble shoot rear wheel bearing damage or wear. If the noise shows itself in the opposite way, then the rear left wheel bearing is damaged.

Rear wheel bearings are not designed at all like front bearings since the rear wheels don’t turn with steering. This is why they will get very loud if they are a bit damaged or warn and you put driving pressure at an angle (in this case by swerving).

If you can get this to happen regularly I think that a mechanic will have a very hard time refusing to ride with you and also to deny to change the rear wheel bearings.

Keep us posted like you have so far and I truly hope this solves your problem. I am disappointed that you have had to do your own trouble shooting on this issue! But I think that you are on the right track to getting to the bottom of this. This last clue you gave us might be the key!

Steve

 

thanks so much for the detailed reply. Im not exactly clear on what side is failing. Let me try describing the situation again.

When driving straight: sound comes only from rear left
Swerving/cornering right: sound amplifies on rear left
swerving/cornering left: sound switches to rear right (but is still slightly present on left)

I truely hope this is the problem so I can get this issue resolved and finally enjoy the car again. I am taking the car in on monday and ill post up my progress with this situation.

 

So it sounds like when you are driving straight, the rear left bearing is already failed enough to make noise, the fact that the sound goes away or gets quieter on the rear left when you swerve to the right is telling me that the bearing is only getting quieter because pressure is off of it. The fact that any noise is coming from the right side when you swerve left is also telling me that the rear left wheel bearing is not too far behind the left side.

This should not happen at all. I had a rear right bearing do this on my Audi that had 280 miles on it when I clipped a curve with that wheel.

Steve

 

okay so I took it to the mechanic and they checked the wheel bearings. They listened with the scope and said they sound fine. So basicaly no luck in finding a solution.

Any more suggestions? I described the sound to a freind mechanic (who lives out of state) and he said its possible that its U-joints or a CV joint? Is this something thats in the 03 E500s?

 

Maybe it's the airmatic suspension, it try to low itself at high speed and something is wrong so it makes the noice.

 

I find it interesting that your dealer was willing to change the differential to try and solve the problem, but now they are not doing anything else even though the problem they first tried to fix is still there.

A wheel bearing that is starting to go will sound totally normal if there is no weight on it. When they listened to it, were the wheels of the ground? If they were, then that is not a real test of the bearings.

If they still are being this stubborn about this I would go to another dealer and complain to MBUSA (not that it will make a huge difference, but it is worth a shot). The problem should only get worse, so they will have to fix it sooner or later. If the problem is finally diagnosed after the warranty is over, then you have tons of proof about this issue and you might still get it covered.

As per the rear CV joints, they don’t make the kind of noise you described when they start to go. But you never know.

Why is your dealer just giving up on the problem?

Steve