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Weird hum noise. Non rpm or speed related

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Old Nov 3, 2021 | 02:24 PM
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Weird hum noise. Non rpm or speed related
I have this weird hum whirling sound that some times comes on at idle then goes away. Most often it comes on while driving and goes away as I come to a stop.
So far I came to understanding that’s it’s not ac compressor, not rpm related and not speed related. The pitch of the sound doesn’t change.
Does not appear to be from the engine bay. Feels almost like it’s the center or back of the car.
08 4 Matic.

Thanks in advance.
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Old Nov 4, 2021 | 01:24 PM
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Any possible modules inside the car that might make a noise? Fans?
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Old Nov 4, 2021 | 08:52 PM
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2010 E550, 273 Engine: 2012 S550, 278 Engine
Do you have multicontour dynamic seats? could be air pump for that.
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Old Nov 5, 2021 | 06:19 AM
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Originally Posted by Arrie
Do you have multicontour dynamic seats? could be air pump for that.
Yes I do have dynamic seats and as far as I know they work fine. I dont have them on most of the time. Just some lumbar settings.
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Old Nov 5, 2021 | 11:38 AM
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Originally Posted by tbilisi79
Yes I do have dynamic seats and as far as I know they work fine. I dont have them on most of the time. Just some lumbar settings.
I just repaired my system. The pressure safety valve of the air reservoir failed and it caused the air leak out and system to go out. My leak was so bad the air pump could not keep up with it at all.

If you have a smaller leak that could produce that sound it could be so small the air pump can keep up with it and not time out from over heating the pump motor.

In my car the pump and reservoir are mounted in the rear seat back on driver's side.
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Old Nov 11, 2021 | 07:47 AM
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THank you. I tried driving the car around with all the seat cushions deflated. Not the source.

I am wondering if tis a fuel pump? Hum starts around 20 mph and goes away when I slow down below 25 or so. Also its not always on but it is most of the time. Noise doest increase in frequency and its not a rhythmic noise. its a dull 650 hz frequency.
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Old Nov 17, 2021 | 08:38 AM
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Anyone?
Noise come in at about 20 mph and stick around till I slow down to 10 mph. Noise comes on most of the time, but some times its not there. Never at idle.
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Old Nov 17, 2021 | 10:23 AM
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Depends on the weather
Unfortauntely, no one will probably be able to tell you with out knowing exactly where it's coming from. Maybe you can do a video and try to capture the sound.
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Old Nov 17, 2021 | 10:37 AM
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Originally Posted by WHPH28
Unfortauntely, no one will probably be able to tell you with out knowing exactly where it's coming from. Maybe you can do a video and try to capture the sound.
Ok thank you.
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