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      04-18-2013, 06:26 PM   #1
Tooyoung00
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Driving with back windows down...

Whenever I drive with back windows down (Either passenger or driver), it makes this loud vibrating sound (like pulsating *sorry hard to explain). it feels like its wind hitting some non aerodynamic surface. It makes driving with back windows down unbearable.

This is stopping me from getting tint because I know the dealer would blame on it.

Is this common?

I remember that some cars have block on the back windows so that it doesn't go all the way down. Is this same issue?
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      04-18-2013, 06:33 PM   #2
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Every car with 4 doors that I've driven has this phenomenon. I don't know the physics behind it, but the simple solution is to just crack your front window an inch when you decide to open the rear windows.
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      04-18-2013, 06:35 PM   #3
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Yep, its wind buffeting. It was worse on my CC.

As noted above, cracking a front window lessons the affect.
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      04-18-2013, 06:57 PM   #4
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Quote:
Originally Posted by Number View Post
Every car with 4 doors that I've driven has this phenomenon. I don't know the physics behind it, but the simple solution is to just crack your front window an inch when you decide to open the rear windows.
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      04-18-2013, 07:19 PM   #5
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Yes its pretty bad, the F30 is the worst I have seen this effect. Normally I drive with one rear window down for the dog.
On my Lexus (RX350) there is no such effect - the only thing you notice is that the radio gets a bit louder.
What I have noticed is that if you open both back windows this helps. Opening the sunroof also reduces it a bit, or a front window (drivers) seems to stop it.
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      04-18-2013, 07:27 PM   #6
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Quote:
Originally Posted by Rolux Magnum View Post
Yes its pretty bad, the F30 is the worst I have seen this effect. Normally I drive with one rear window down for the dog.
On my Lexus (RX350) there is no such effect - the only thing you notice is that the radio gets a bit louder.
What I have noticed is that if you open both back windows this helps. Opening the sunroof also reduces it a bit, or a front window (drivers) seems to stop it.
Obviously it's because of BMW QC problems

/sarcasm

Probably just different window geometry...the design folks likely overrode something a pimple faced engineer suggested after wind tunnel testing.
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      04-18-2013, 09:09 PM   #7
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With back windows open the wind builds up a pressure toward the back of the car but there is no outlet, the pressure builds untill it is higher than the incoming air pressure causing it to spill back out against the incoming flow-this happens repeatedly and causes the buffeting-you may also notice your ears feeling it.
Solution is to have one window open, the other side cracked so the high pressure on the open side can escape on the low side.
It's even worse with the sunroof open and no windows open, again cracking a back window lets out the pressure.
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      04-18-2013, 09:15 PM   #8
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When i drive, in a nice awesome day, i would like to pull all my windows down also the pano roof and enjoy teh Sun and Chicks Winking
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      04-18-2013, 10:20 PM   #9
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Quote:
Originally Posted by Rolux Magnum View Post
Yes its pretty bad, the F30 is the worst I have seen this effect. Normally I drive with one rear window down for the dog.
On my Lexus (RX350) there is no such effect - the only thing you notice is that the radio gets a bit louder.
What I have noticed is that if you open both back windows this helps. Opening the sunroof also reduces it a bit, or a front window (drivers) seems to stop it.
You haven't driven enough cars then (just comparing it to the RX350 doesn't really qualify you to say it's the "worst"). I've driven fords, Nissans, Hondas, Audis, and it all depends on the window shape and how far you have it down. The F30 is no better and no worse than any other car out there, you can't change the laws of fluid dynamics with a car. Next time roll it up or down a bit more and check out the difference it makes.
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      04-18-2013, 11:16 PM   #10
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Not an expert, but it probably has to do with either high/low pressure or air speed associated with a fast moving vehicle. As others have said, crack a front window, or what I like to do, vent the sunroof.
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      04-19-2013, 12:38 AM   #11
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vent or open the sunroof... and crack one of the rear windows...

I always do that...

that prevents the pulsating wind noise...
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      04-19-2013, 01:07 AM   #12
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If we are talking all windows down the middle backseat seatbelt vibrates due to the wind and hits against the back seat.
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      04-19-2013, 07:51 AM   #13
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I've noticed that on all cars I've been in since I'm a kid basically. Is the F30 the first car you've ever been in?
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      04-19-2013, 08:55 AM   #14
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It's turbulance/resonance depending speed, quiet normal. Answer already posted by "Number", like opening one of the front windows an inch for handling air pressure. Also opening sunroof helps. The same (normal) phenomenom happens on fully opening (twice sliding button) the sunroof with all windows closed. (that's why 2 stage designed)
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      04-19-2013, 10:55 AM   #15
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I understand its some air going in and some air trying to escape at the same time
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      04-20-2013, 06:29 PM   #16
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Quote:
Originally Posted by jacar View Post
With back windows open the wind builds up a pressure toward the back of the car but there is no outlet, the pressure builds untill it is higher than the incoming air pressure causing it to spill back out against the incoming flow-this happens repeatedly and causes the buffeting-you may also notice your ears feeling it.
Solution is to have one window open, the other side cracked so the high pressure on the open side can escape on the low side.
It's even worse with the sunroof open and no windows open, again cracking a back window lets out the pressure.
Same in many cars with sunroof, cracking rear windows stops the buffeting.

My E91 and F11 with panoramic roof always need the rear windows cracked open if I drive with a fully open roof at anything over 30mph.

Had many cars over the years with a sunroof and all the same to some degree.

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      04-21-2013, 04:30 PM   #17
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i will say that i experienced the loudest standing wave phenomenon ever in my car this past weekend.
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      04-22-2013, 11:19 AM   #18
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Quote:
Originally Posted by ft1338 View Post
I've noticed that on all cars I've been in since I'm a kid basically. Is the F30 the first car you've ever been in?
HAHA no. This is my 3rd 3Series. Always drove coupe. This is my FIRST sedan. So I had no idea..... Damn you 4series!!
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      04-22-2013, 05:00 PM   #19
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Quote:
Originally Posted by Tooyoung00 View Post
Whenever I drive with back windows down (Either passenger or driver), it makes this loud vibrating sound
Is this common?
Yes. Had the same issue with my E90.

Quote:
Originally Posted by Tooyoung00 View Post
This is stopping me from getting tint
Get your car tinted. It's great. Don't let this worry you.
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      04-22-2013, 06:11 PM   #20
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Quote:
Originally Posted by Tsuyoi View Post
You haven't driven enough cars then (just comparing it to the RX350 doesn't really qualify you to say it's the "worst"). I've driven fords, Nissans, Hondas, Audis, and it all depends on the window shape and how far you have it down. The F30 is no better and no worse than any other car out there, you can't change the laws of fluid dynamics with a car. Next time roll it up or down a bit more and check out the difference it makes.
Obviously I have noticed this effect before on other cars - see my garage for details of what I have been driving for the last 10 years

Perhaps there are other cars that are worse - I just have not been in them.
The F30 is pretty severe - the dog insists on the LHS rear window all the way down, and even at 30mph is is bad. Not that it worries me - I just open something else. Usually everything else, and turn on the heated seats.
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