Very strange 124 wagon noise.
 

Bought a 95 E320 wagon two weeks ago. Nice car.

Driving town yesterday about 30MPH I open the sunroof for the first time.

Thump! Thump! Thump! Hell of a noise. I thought something had broken.

Close the roof, noise goes away.

Open driver and passenger window. No noise.

Open either rear window. Hear the noise.

Open sun roof halway. No noise. Only hear it if opened all the way (or near).

Very strange. It is speed related, slows down as car slows down, and vice versa.

Has anyone had anything close to same symptoms?

Thanks.

I've not seen any posts on this, but every benz I've owned from the first 76' 300D thru a 92 TD 4matic had some wierd harmonic vibration with the roof open and no window cracked down a bit. My first guess is the sliding headliner has come loose in some way, and while it retracts properly when the roof is opened (right?); wind causes it to flap around.

Next guess is the roof itself not staying tightly in the track when fully open.

In either case, it takes a combination of speed and air pressure to set the vibration up.

These are adjustable issues, and the appropriate shop manual if you are a DIYer should give you the answers.

Try setting your A/C to EC mode and low speed fan. Allow some extra air to enter the passenger cell and you will reduce the vacuum that is caused when the sunroof is opened fully.

It is resonance
 

Your car becomes a "tuned chamber" and the airflow resonates. Lots of cars do it. You may be able to stop it by cracking open a window, in addition to the other suggestions.

Rgds,
Chris W.

If your roof rack has the cross bars installed they cause alot of wind noise. Try removing bars to see if noise goes away.

To avoid the 'drums' we all get with the windows closed, I bring my roof forward about 1 inch. Works like a charm. Maximum opening requires a window cracked in every sunroofed car I have ever driven.

Modern cars all will "drum" badly with only one window open. Even my 85 Volvo is bad, have to crack the opposite rear window to keep the wind from drumming into my years. The W124 blows directly into my ear from behind with the windows open!

Crack a window, the noise goes away. It's the price we pay for such clean aerodymamics.

Peter

After driving Mercedes-Benz wagons for almost 20 years I have found that both, on S123s and S124s, when you open the sunroof completely or just open ONE of the rear windows without opening the roof or any other window, you get a terrible "thump" noise which worsens as speed increases.

As commented before, is because the car becomes a tunned chamber as air resonates. Funny the M. B. wagons (all of them) respond in the same way. I do not have this problem with my V140.

If you closely inspect the chromed bar that runs under the sunroof on both sides, you will see at the end two drilled marks. If you fully open the sunroof, the front edge of the roof will pass over this marks.

Slide the roof back a little so the front edge of the roof aligns with the first mark (for slow or town speed driving) or with the second mark (for fast / highway speed driving). You just sacrife maybe 1/2 an inch to an inch, but it really works.