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WIND NOISE when rear windows are rolled down

9 messages,  Last post on Jul 09, 2008 at 10:03 AM

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#1 of 9
WIND NOISE when rear windows are rolled down by 2008car
Jul 03, 2008 (5:21 pm)
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I have loud wind noise when the rear windows are rolled down. Its like a decompression and recompression of my ears. Is this normal. Its a new Rav4 08.
 
I'm not sure how to explain it but you can not roll down the windows with out hearing the noise.
 
Its a fast pu pu pu pu pu pu pu pu sound.
 
This happens when i start hitting 40 miles an hour on the freeway.
 
Is this normal?
#2 of 9
Re: WIND NOISE when rear windows are rolled down [2008car] by wwest
Jul 03, 2008 (5:33 pm)
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Replying to: 2008car (Jul 03, 2008 5:21 pm)

"Is this normal?"
 
Absolutely,...SOP..!
 
Think of blowing a whistle..
 
When you roll down that window "at speed" it's like blowing across the top of a coke bottle, except at 40 MPH the airflow across the bottle top is much higher and the back of your car has a LOT more volume, so the "whistle" frequency is really LOW, in the range of a helicopter blade.
 
Cracking a front window as little as 1/2" will usually alleviate the "noise".
#3 of 9
Re: WIND NOISE when rear windows are rolled down [wwest] by sdc2
Jul 07, 2008 (11:33 am)
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Replying to: wwest (Jul 03, 2008 5:33 pm)

Yep...it is basically an infrasonic whistle. The RAV does it pretty bad, but I have heard it in many other vehicles as well.
#4 of 9
Re: WIND NOISE when rear windows are rolled down [sdc2] by tidester HOST
Jul 07, 2008 (11:50 am)
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Replying to: sdc2 (Jul 07, 2008 11:33 am)

it is basically an infrasonic whistle
 
If it were infrasonic then you wouldn't hear it.
 
tidester, host
SUVs and Smart Shopper
#5 of 9
Re: WIND NOISE when rear windows are rolled down [tidester] by wwest
Jul 07, 2008 (3:20 pm)
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Replying to: tidester (Jul 07, 2008 11:50 am)

Hmmm...
 
Then it could be infrasonic....
 
Do we actually hear it or do we really only feel the air pressure waves...??
#6 of 9
Re: WIND NOISE when rear windows are rolled down [tidester] by sdc2
Jul 08, 2008 (5:52 am)
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Replying to: tidester (Jul 07, 2008 11:50 am)

The beat of this effect is less than 10 cycles per second...it is generally assumed that people cannot "hear" sounds below 20 cps and based on my audio experience even this is optimistic. But you can definitely feel it in your head and ribcage. There is a slight bit of noise associated with each beat, I am unsure if these would be considered harmonics, or more likely just produced by turbulence around the window edge (a more perfect whistle would have sharper edges at the opening).
#7 of 9
Re: WIND NOISE when rear windows are rolled down [sdc2] by tidester HOST
Jul 08, 2008 (10:14 am)
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Replying to: sdc2 (Jul 08, 2008 5:52 am)

I am unsure if these would be considered harmonics
 
That would be a good bet. It's quite easy to get a flute to produce harmonics when you up the amplitude a bit. And if the amplitude of the oscillation in the RAV4 is great enough to feel then you're probably above the threshold to produce harmonics.
 
tidester, host
SUVs and Smart Shopper
#8 of 9
Re: WIND NOISE when rear windows are rolled down [tidester] by wwest
Jul 09, 2008 (7:31 am)
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Replying to: tidester (Jul 08, 2008 10:14 am)

But then there is the "vibrations" effect the air pressure waves cause on the interior materials and surfaces.
 
That might be, predominantly, what we "hear".
#9 of 9
Re: WIND NOISE when rear windows are rolled down [wwest] by tidester HOST
Jul 09, 2008 (10:03 am)
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Replying to: wwest (Jul 09, 2008 7:31 am)

Possibly but I don't think we've actually established whether the "sound" is infrasonic and more input from the OP would be helpful. It could just be audible low frequency sound. In any case, it's probably just the ubiquitous "helicopter" effect with sound being produces with pressure changes occurring at the window opening.
 
tidester, host
SUVs and Smart Shopper

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