Name that sound... - PeachParts Mercedes-Benz Forum

TWeatherford · #1 10-27-2007, 11:23 PM

Hey folks. I need some help diagnosing a strange whining sound coming from my car. I have owned the and driven the car for the last 10K miles, and heard this noise about three time for a very short time (each time I was going slow - under 30 mph, and it was literally for less than 10 seconds) so I didn't worry about it. Yesterday, it showed up and appears that it is not going away.

Here's a video that you can hear it on.
http://video.google.com/videoplay?docid=-722875362697214804

I haven't found out if it goes away above 50 mph, cause I didn't want to cause any extra damage. I'm thinking it might be the driveshaft. I did swerve kinda hard back and forth and it didn't change, so I'm thinking its not a wheel bearing. The transmission fluid is full enough and pink, and shifts perfectly so I don't think its that. The noise comes, and sometimes cuts out really abruptly, other times it gradually fades as I slow down. Any help?

kerry · #2 10-28-2007, 09:31 AM

Don't know what it is. Have you checked the differential fluid?

TWeatherford · #3 10-28-2007, 10:32 AM

You know, I haven't checked the differential fluid. I'm at college, so its kinda hard to do anything on the car right now... I just work on it when I'm at home weekends. I do know that the previous owner replaced the rear differential with a brand new one in the last 50K miles, so I haven't really worried about it.

pawoSD · #4 10-28-2007, 10:38 AM

I agree, CV axle or Differential is making the sound. Our 300D whines a bit too when under throttle at above 50mph. I changed the diff fluid, which was CLEAN!

First time I've ever had that happen, I guess it was indeed well maintained.

Anyways, ours has had a whine (not as bad, but similar) to yours for over 3,500 miles so far....and always above 50-55mph.... but at like...65-70+ it goes away.

TTCummins · #5 10-28-2007, 11:03 AM

Yeah sounds like a gear whine or a driveshaft from the video anyway. Can you feel any vibration through the gear selector or through the body at all?

TWeatherford · #6 10-28-2007, 07:12 PM

I can't feel any vibration... I'll crawl under there tomorrow and see if there is any play in the driveshaft.

pawoSD · #7 10-28-2007, 07:14 PM

If something was bad on the driveshaft my bet is you'd have some major vibration. I had a lot of vibration just from a bad Center Bearing support....and my flex discs were nearly at deaths door. Good thing I replaced them!

Gil · #8 10-28-2007, 07:23 PM

I once had a TR7 that developed a whine kind of like that, in the transmission. Over the course of a trip it got louder and louder, till the tranny just locked right up. It was all I could do to push in the clutch pedal and drift to the breakdown lane (also known as a parking lot for British car owners). It was a manual tranny, tho, so I don't know that you're about to experience the same fate, but that noise just brought back some serious nightmares.

vstech · #9 10-28-2007, 08:14 PM

wow, that is a bad noise... it sounds like a tire hitting something but I don't think a tire would last long that way. does your car sit low? do you have any noises on hard left or right turns? are there any noises when in reverse under heavy acceleration? that loud a noise could be anything... go ahead and push past 50 and see if it continues to get louder or if it stops. be prepared for it to lock up and break though. in other words don't do it in traffic, and have someone nearby to assist you in the event that something goes horribly wrong...

TWeatherford · #10 10-28-2007, 11:50 PM

The noise does sound worse on the video. Took the car out today, and over 50 it isn't really there, or if it is its very faint. My car does sit low in the rear, mainly because I'm a college student and have all my junk (tools, etc) in there. It isn't a tire hitting something. I'll try and crawl around under it tomorrow and see where anything might be rubbing. It does sound like its coming from the transmission, I won't rule out something around the rear axle but it definitely sounds like its coming from near the shifter. Man it would stink if my transmission locked up...

TWeatherford · #11 10-31-2007, 09:39 AM

I haven't done a transmission filter and fluid change since I bought the car, about 10K miles ago. It was well maintained by the previous owner and I haven't gotten to it. Is the filter possibly so plugged that fluid can't get where it needs to in the tranny? Do you think a simple change, with some nice new synthetic in there might help?

Any tips on how to rule out cv joints?

I'll change rear diff fluid to make sure thats not it.

Sparing that, I guess its off to pull-a-part to buy a transmission. Only thing with that is they don't allow jacks, how am I supposed to get the tranny out without jacks? I think I'll be able to pick the transmission up myself, but won't be able to lift the whole car to get it out from under there. Of course then I'm getting a tranny I know nothing about, maybe I better pick up two while I'm there since I have to drive 4 hours to get there.

This would be simpler if I wasn't at college, 180 miles away from home. I'll probably have to get it towed home, I don't want to risk locking this thing up on the highway with four semis bearing down on me on I-65, like they seem to do a lot.

I'm also going to look around town here and see if there's an indy mechanic that might be able to take a look at it.

Any other suggestions?

JimSmith · #12 10-31-2007, 11:35 AM

The pitch of the noise appears to be speed related, meaning as you increase speed, the noise increases in frequency. This is typical of drive line noise as opposed to, say, an exhaust leak. I had a 1975 240D with some pin-holes in the exhaust that would whistle under certain flow conditions and once they were whistling, and it was an ear-piercing whistle that could be heard for long distances, the frequency stayed the same, only the amplitude (loudness) changed with throttle position or speed. At highway speeds the conditions for making the whistling noise disappeared and whistling went away, but on my way to work before getting to the highway I am sure I woke up many a neighbor.

Anyway, you might want to see what speed the event happens in other gears besides Drive. If changing the rpm of the engine and transmission bits has no effect on the car's speed when this happens, it is likely a drive-line only problem. It may still be an output shaft related problem with the transmission, but if the transmission fluid is in good shape I would find that less likely than a center support bearing or a differential problem. You also need to understand if this is load related. Try to find a hill to run up in a few different gears and loads to assess the engine/transmission vs. drive line, and then load sensitivity of the origin of the noise.

The CV joints don't really have a mechanism to make a whine type noise and in my experience when they fail they make an alarming crackling noise that comes and goes with load and speed. Load does not seem to be the instigator here, but the CV joints are definitely a load sensitive in my experience (more load makes the noise, less load makes less noise, and sometimes very low load makes the noise again, as the joint is given a degree of freedom to wobble that it does not have by design). Early differential wear can also be load sensitive in that at very low loads the combination excitation frequency and load dependent friction can bring about a differential whine much like the way you rub a crystal wine glass with a wetted finger with the just the right speed and pressure will make the wine glass sing.

Any significant change in pressure (load) disrupts this mechanism and the noise goes away. In my cars when this happened I changed differential fluid to a RedLine "Shockproof" product and that seemed to also disrupt the mechanism at the oil film interface. It is not the end-all for differential whine, but it does make it change where in the car's speed range the noise appears.

In any case it would seem the noise is not a healthy one, and it is likely worth the effort to track it down and fix it. Good luck, Jim

Gil · #13 10-31-2007, 01:46 PM

You can probably rule out CVs, as it doesn't sound like the typical grinding noise you get from a CV that's on the brink of destruction. To be sure, drive the car in a wide open parking lot at low speeds and go in a circle one way, then the other. Listen for noises up front (wheel bearings) and in the rear (CVs) if you notice a grind or a change in noise either way, there's your answer. However, since this appears to be happening at moderate highway speeds, it's more likely to be a tranny problem.

A filter and fluid change is not too hard to do and doesn't cost much. It certainly won't hurt anything. Can't speak from experience with the synthetic fluid, but I hear it's nice.

spugeddy · #14 10-31-2007, 02:05 PM

I am in the middle of a CV replacement today.

If it were CV trouble you here more metalic sounds and rythmic thumping, like a troll is under your back wheel thumping the body with a mallet. crawl under and look at the inner and outer boots. Mine were ripped on both ends, but my noise was way different....could he have a brake caliper stuck... do you get heat and brake smell back there....

Or does it sound like it is coming from the middle/center of the car...

TWeatherford · #15 11-01-2007, 08:54 AM

Thanks a lot guys. I have checked out my CV boots and they look great, and I am not having any thumping, so I'll rule that out. I drove the car again yesterday. I tried it going fast in reverse, nothing. As I drove, it wasn't very prominent, and it still sometimes just goes away abruptly. It is very faint, but it sounds like a large engine or centrifuge spinning down as I ease to a stop from 30 mph. Putting it in neutral doesn't change much. I'm going to change the rear diff fluid, then the transmission fluid and filter, and see if that changes anything.

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