For those who might experience a weird noise at about 10 seconds apart that came from the right rear of the vehicle, I have an interesting fix for you! This noise is coming from the vacuum pump located at inside the right rear panel under the trunk cover.

When the noise is heard especially when the air conditioner is running, turn the internal door lock switch on and then off. May have to repeat acouple of times to get the effect.

It got rid of my problem until next time I started my car.

Ultimate fix? I need advice!

It is still not clear to me what type of weired noise you have. You possibly have the W126 body which has the pump inside the trunk. My wild guess is that you have an air leak. Therefore, the pump is working extra hard to compensate for the problem.

David

Thank you for the tip David. I think there is a leak on the vacumme hose under the dash which may have caused the air didn't flow through center vents correctly.

How do I find this leak? Thanks for your vaulable advice!

Golden

For the vent problem, it is either the vacuum servo or disconnected/broken hoses. Visit the following link to see it it helps. I heard, two years ago, there was an after market rebuilt kit available for the servo, about $5.

300SD stuck on DEFROST

David