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      02-27-2014, 01:34 PM   #1
MetaX
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Strange suction sound on 35i?

I've been hearing this noise coming from the engine bay ever since I bought the car but haven't gotten around to asking this question or searching for it (no relevant results found). It isn't much of a bother to me as it doesn't seem to affect performance, is infrequent, and I only hear it when I drive with my windows open but if it is unique to my car I might want to have it checked out while my car is clinging to the last scraps of its warranty.

When accelerating from a stop--particularly when accelerating mildly while going up a hill (like a parking garage ramp)--I hear this odd suction/sucking noise. It's hard to describe but it sounds like sucking in your breath, mouth in an O-shape, with the back of your tongue rolled up towards the roof of your mouth. It is quite loud and my only hypothesis is that the air going into the throttle body is being affected in some way that is causing turbulence or noise. With greater acceleration or WOT the noise is non-existent so I suppose that the sound is coming from a combination of the restriction, subsequent alteration of air flow path, and unique resonant properties of the intake. Is anyone else experiencing this on their 35i?
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      02-27-2014, 02:54 PM   #2
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Have never heard it on our 2011 35i. I'd point it out to the dealer on the next service; might be an air leak.
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      03-21-2014, 08:23 AM   #3
hillanddale
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Reminds me of taking off the air cleaner on a four barrel when I was a kid. Made it sound fast.
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      03-21-2014, 08:41 AM   #4
fjrmann
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have you opened the hood and worked the throttle with your hand to hear this noise?
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      03-21-2014, 09:55 AM   #5
n55x3
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The N55 underload will exhibit some noises as you describe as the turbo is depressurizing when you lift off throttle. In the past this was handled by something called a BOV - blow off valve. The N55 motor has an electronically controlled valve called a diverter valve.

Anyway, this is normal. You can't always hear it under WOT as the exhaust and engine noises become much louder than the DV releasing pressure. Some folks try to replace stock BOVs (where applicable) to amplify this sound.

And in regards to working the throttle with your hand under the hood, that's not going to happen. It's all electronic. The days of tugging on a throttle line while under the hood are long since gone unfortunately.
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      03-23-2014, 10:44 AM   #6
fjrmann
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Quote:
Originally Posted by n55x3 View Post
And in regards to working the throttle with your hand under the hood, that's not going to happen. It's all electronic. The days of tugging on a throttle line while under the hood are long since gone unfortunately.
Thanks, I thought there may have been some way. Guess if I need to hear the motor rev in the future, gotta get someone to work the accelerator pedal.
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      03-23-2014, 08:55 PM   #7
toughen
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i may know the sound you talking about, i have x3 3.5i, if i use sport mode, and if i accelerate slowly, i can make this shound come out every time i wanted to....
it happens when rpm hit 2-3k. sounds like you sucking a empty bottle...
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      03-24-2014, 09:58 AM   #8
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Quote:
Originally Posted by toughen View Post
i may know the sound you talking about, i have x3 3.5i, if i use sport mode, and if i accelerate slowly, i can make this shound come out every time i wanted to....
it happens when rpm hit 2-3k. sounds like you sucking a empty bottle...
It is likely either the turbocharger spooling up or the blow off valve activating. The sound being described sounds like normal turbocharger operation.
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      03-24-2014, 04:46 PM   #9
toughen
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Quote:
Originally Posted by Barbera335 View Post
It is likely either the turbocharger spooling up or the blow off valve activating. The sound being described sounds like normal turbocharger operation.
i like the whistle sound, but not this sucking noise... lol
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      03-27-2014, 09:52 AM   #10
drlukas
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Could be the same problem http://x3.xbimmers.com/forums/showth...smission+noise

It sound like cow moo, No solution for Bmw
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