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View Full Version : Weird Open Rear Windows 'Strobing' Effect


Sans Nil
01-28-2008, 09:50 AM
I rarely have only the rear two windows down and the front/moon roof closed but this weekend I had occasion to when trying to air out my 2007 X3 after sucking in fumes from a nasty grease truck that had been in front of me. It reminded of something that I experienced when I first got the car and forgot about until now.

When I drive with just the rear two windows fully down there is a strangely disturbing audio “strobing” effect that manifests that hurts the ears. I was glad to have a passenger this time as otherwise I would think I might be having a stroke, but she heard/felt it too. The oscillating vibrations seem to occur when on different road surfaces and as long as your at a decent speed or higher. The effect diminishes as you close the rear windows and disappears completely at a certain point of partially open. Has anyone else seen this in their X3? I know it's probably rare to have just the two rear windows down and the others up but I'm really curious if my X3 just happens to have the right combination materials to do this or not.

It's not really a major issue, just really odd! Anyone heard of something like this before?

Andrew*Debbie
01-28-2008, 12:02 PM
"They all do that." Well at least ours does. So did our 2004 325i.

The fix as you have noted is to adjust the windows.

Bamafn1
01-28-2008, 12:10 PM
Pretty much every car I've ever driven has done that. "Normal"!

nyccarguy
01-28-2008, 08:59 PM
Definitely normal. To get ti to go away, either crack one of the front windows or Tilt the sunroof up.

archrenov8
01-29-2008, 05:19 AM
That is what is known as buffeting and it is very common. It has to do with aerodynamics, and how the air moves over and around the body, and comes in and out of the cabin. people also get buffeting from having a sunroof open all the way, without any windows open. Same issues, same solutions.

X3 Skier
01-29-2008, 05:59 AM
Its basically the same thing as when you blow across a pop bottle to make a noise. Sometimes called the Helmholtz Resonator effect. Likely the reason the moon roof has two positions.

Cheers

Bamafn1
01-29-2008, 08:13 AM
Its basically the same thing as when you blow across a pop bottle to make a noise. Sometimes called the Helmholtz Resonator effect. Likely the reason the moon roof has two positions.

Cheers

Very scientific!

iversonm
01-29-2008, 08:15 AM
Its basically the same thing as when you blow across a pop bottle to make a noise. Sometimes called the Helmholtz Resonator effect. Likely the reason the moon roof has two positions.

Cheers

Yes, you've made your car into a giant whistle.

Sans Nil
01-29-2008, 09:42 AM
Wow, thanks everyone, I can't believe I'd never encountered that before.

I really need to get out more it seems.

Of course, with the air in LA it probably explains why my windows are up most of the time.

;)