Strange noise coming from the dash

The car: 1980 300TD wagon

The problem: VERY loud noise (at least 70db) coming from the left area of the dash (drivers side since its an american make) based on speed. I do not think its based on RPMs but it might be, I revved it in the parking lot earlier and didnt get the noise. Then later driving it would come on about 40mph VERY loud and not get louder as car went faster, but would quiet down when speed was decreased. Its not wind based I do not beleive because it stays loud no matter what direction Im driving and there was no wind out tonite as well. In addition, when the car got all heated up, it would take longer to kick in, about 15 seconds of steady 40+ mph driving for it to come on.

What the HELL is this? I've never heard of something like this before.

Tony

Oh and the noise is kind of like a constant alarm siren, that does not change pitch unless the speed changes.

[Robert W. Roe]

A few wild guesses... speedometer cable, driveshaft center bearing or U-joints (though the location is wrong, these noises are speed sensitive), or maybe a mouse built a nest in your HVAC ducts? Does it go away if you turn your climate control off?

No it stays no matter if climate control on or off. It JUST started tonite when I took her for a short trip to taco bell.

It may just be temp related because its been colder today than almost any other day since I got the car and the noise did act differently after she warmed up a bit.

Who knows?

Its gotta be a vacuum leak, because I know this car had at least 1 already because the doors act very peculiar (locking sometimes, sometimes taking a long long time to lock, etc) maybe it developed a worse one now.

I figured it out, whenever it makes that noise the speedometer goes bezerk twitching. I'll need to rip the panel out and replace something Im sure in the future, but right now Im not messing with it as it only does it in really cold weather.

Tony

[leathermang]

Well, leave it to someone not from Texas ( and proud of it ) to run across one of our most insidious pests... the dreaded instrument panel Vole... related to rats but deathly afraid of clacking noises and traveling fast... be sure to use heavy gloves when you go in after it... Greg

[lrg]

I once had this exact problem with an old Peugeot diesel. It was the Speedo cable. When it was cold it was worst but as things warmed up it usually went away. It was a Gawdawful noise. Try squirting a little graphite down the cable and if that doesnt work you should be able to withdraw the inner cable and inspect/oil it. Mine was dry at the top toward the instrument cluster and binding (my speedo also went wild...was due to inner cable binding). If you oil it use graphite because if the lube is too heavy it will cause the cable to bind slightly and the speedo needle to wander, but not something too light either or it will just run down the cable and dry out again. If its kinked, you'll need to replace the inner cable (usually the outer jacket is fine) and you can get those custom made at a speedo shop for about $40-50. Bring your old inner cable in as a template. I've gotten them back in from the instrument end by just gently spinning it as I feed it in. As you get to the end you should be able to feel the transmission end engage as you slowly turn it. Other than getting at it, it should be an easy job. Good luck.

[Luke]

Disconnect the speed-o cable from the VDO and then reseat it. Mine did the very same thing last Monday morning. At about 35 MPH it started to scream, and I could feel the instrument panel glass vibrating. When I got the car up to 70 the sound vanished, until I stopped at a light, and increased speed again. Anyway, when I got to work, I quickly pulled the panel, reseated the cable connection, and it has been quiet since. That noise sure scared the hell out of me for a few seconds. It's loud.

Luke

What do you mean by reseating it? Is it pulling the cable out and push it back in? Thanks...

[P.E.Haiges]

In my 300SD, the screeching noise was the speedometer itself. It happened on a day cold too.

That was a long time ago. I got the speedometer fixed and its been OK since.

P E H

PEH...How did you fixed your speedometer? What wrong with it? Is it a do it yourself job? Thanks...

[P.E.Haiges]

300cd,

I was on my way to Vegas when the noise happened on a cold morning. I removed the cable to stop the screeching noise because I thought the speedo might be damaged further.

I was driving on LasVegas Blvd and I saw a speedo shop (not there anymore). I stopped and asked about fixing speedo and was told to bring it in. So in the parking ramp, I took out the instrument cluster, removed the speedo from the cluster and took the speedo to the shop. A day or 2 later and $35, speedo was fixed.

That probably was 10 years ago and its been working fine ever since and its accuraturacy is less than 1% off, both speed and distance.

When you put the cluster back in, make sure you don't get a kink in the cable. I did and the cable broke and I had to replace it.

P E H

[dpbrowne]

My 83 300SD was making a noise that sounded like a fan problem (ratteling) at certain speeds. It turnd out to be a broken support bolt on the air filter.

[db07974]

My 95 300d was just picked up from the mercedes shop for glo plugs, new serpentine belt, new disc. Driving it home, I noticed if I go over 40 mph it makes a siren-like noise that specifically comes from the dash of the driver's side.

Did you ever find out for certain what it is? It was not like this when I brought it into the shop.