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What is noise coming from vents?

Tiny
COMPTECH61
  • MEMBER
  • 2002 MERCEDES BENZ ML500
  • 137,000 MILES
I hear a strange 'blowing'-air circulating with a different pitch then the ac from the vents. When I apply the breaks it stops. I was told possibly blend door? Possible or something else? The ac does blow cold. I haven't tried to switch it o the heat yet cause las Vegas is hot enough, lol. What can it be? How can I verify the problem? What would it take to fix it? Where is bad part located? Many thanks for the help
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Tuesday, September 11th, 2012 AT 8:38 AM

10 Replies

Tiny
ASEMASTER6371
  • MECHANIC
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Does it make the noise with key on, engine off?

Possible vacuum leak

Roy
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Tuesday, September 11th, 2012 AT 11:56 AM
Tiny
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I am not sure. Didn't try it. Will check today. If it happens with engine off/key on is that the vacuum leak or the other way around?
Thanks for the response
Alan
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Tuesday, September 11th, 2012 AT 12:16 PM
Tiny
ASEMASTER6371
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Vacuum leak if the noise is gone

Roy
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Tuesday, September 11th, 2012 AT 12:43 PM
Tiny
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And if the noise is still there? Could it be blend door as was suggested or is there anther possibility?
Again thanks
Alan
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Tuesday, September 11th, 2012 AT 12:57 PM
Tiny
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Possible but lets start somewhere and not guess
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Tuesday, September 11th, 2012 AT 1:25 PM
Tiny
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The noise only happens with engine running. It sounds like it is only on drivers side
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Wednesday, September 12th, 2012 AT 2:21 AM
Tiny
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And coming from under the dash, not from the vents
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Wednesday, September 12th, 2012 AT 12:52 PM
Tiny
KHLOW2008
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You have a vacuum leak somewhere and need to locate the source.

Noise stopping when applying brakes could mean a fault with the brake booster or related components.
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Wednesday, September 12th, 2012 AT 2:06 PM
Tiny
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I have driven the truck and the brakes seem fine. No problems stopping nor spongy. Could it still be the break boster or what other possibilities can it be? Sounds like it could be expensive to fix? Or can I be lucky and have a bad or unconnected vacuum line?
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Thursday, September 13th, 2012 AT 3:26 AM
Tiny
KHLOW2008
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It is possible to be a vacuum leakage somewhere but without further probing, you can't be sure.

If it is a brake vacuum, it won't become spongy, instead more pedal effort is needed and repeated pumping of brake pedal would result in a stiffer pedal.

When you try to start vhicle after starting, before you tirn ignition on, test if the brake pedal is soft or stiff.
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Thursday, September 13th, 2012 AT 7:16 AM

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