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Marty, ASE Certified Technician
Category: Mercedes
Satisfied Customers: 54972
Experience:  Bosch Certified Master Technician with over 35 years experience in the automotive industry.
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Loud whining sound inside car when engine is on. can not

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loud whining sound inside car when engine is on. can not locate source
stops when door is open. started yesterday
w114 1973 280ce

Hi, my name is***** sounds like you are describing a vacuum leak from inside the car. The noise could be coming from the driver's door lock or one of the other locks. You can disconnect the yellow vacuum line under the hood next to the brake booster that feeds the vacuum door locks to see if the noise goes away.

Let me know what you find.

Customer: replied 1 year ago.
disconnected yellow vacuum line sound stopped then started again while still disconnected

If you only hear the noise when the engine is running I would have to suspect you are hearing a vacuum leak inside the car. You can try disconnecting the other vacuum lines that lead into the cabin and see if the noise goes away. If you hear the noise with the key on and the engine off I would suspect an electrical noise. If that is the case I would try cleaning all of the fuses. You might be hearing a faint sound from the door ajar buzzer.

Customer: replied 1 year ago.
only hear it with engine on
how do i find cabin leak and fix it?
First you need to determine if it is a vacuum leak that is causing the sound. Since I cannot hear the noise I need you to disconnect all of the vacuum that goes into the car to see if the noise goes away.
Marty and other Mercedes Specialists are ready to help you
Customer: replied 1 year ago.
started car today no sound! ?

Okay, if everything is okay with the vacuum lines disconnected I would suspect a leak in the vacuum system for the door locks.