Whistling sound fan / heater

[BG500]

I have an issue with a whistling sound in the car, it's coming from the driver side air vent and is driving me crazy
I started to notice this as soon as the temperature started to drop in the autumn, but now we have 10 below zero Celsius and it's no longer something I can ignore.
The sound is directly linked to the fan speed , so as soon as the engine heats up and the climate control increases the fan speed, the sound goes up.
I can also force a manual increase/decrease by running the fan manually up or down. It doesn't change if I manually change the air direction (floor, center console or windshield) or if close the air vent.
It also changes tone /pitch every time I pass a car coming towards me in the opposite lane, which is extra fun to listen to...
so I have constant "psssiiiii" interrupted by a quick "psiuuu" every time I meet someone going in the opposite direction.
However it goes quiet if I open the window by just a fraction.
My current theory is that the air duct located somewhere behind the rear bumper is blocked and not letting the air escape, so the fan builds up pressure inside the cabin. But this is not based on any facts, apart from that it goes quiet with the window down.

The car is going to the dealer next week but I'm not to optimistic they will find and resolve the issue.. so any tips or suggestions are greatly appreciated

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[Karacticus]

With oncoming/passing traffic affecting the noise, it may be useful to know if things change if you manually select recirc or fresh for the air source.

Other ideas to throw at the wall— has the cabin air filter been changed? Might be worth looking into whether the filter box has been closed back up correctly.

l’m also not sure how the air intake drains on this car, but on my old Z4, the cowl area drained into the engine bay through a device with loosely fitting flap on the end. If there’s debris in the flap, I could see that whistling with pressure changes.

Also, does it go away completely if you shut the fan off? I will say that BMWs tend not to have the quietis blower motor bearings.

 

[XtremeMaC]

Ahh the whistle noise. Brings back memories... You may be surprised of how a little gap may be causing this and judging by your explanation it sounds as though the rubber/plastic shrunk enough to open the gap between flaps and housing or small misalignment. That's my theory anyhow...
Vehicle isn't airtight, so rear flaps probably isn't the issue. You'd probably have door closing and pressure on your ear if that was the case and probably fogging as well since it's cold out... But still interesting to hear it goes away with window. Happens even when you're stationary?
Driver side air vent as in the one next to the windows?
Did you try to block the one specifically for the window? Try putting a tape on it. Pull the register out. Not sure how it's attached on this vehicle..

 

[BG500]

Hi guys, thanks for the input??
To answer all above ;
Manual recirculation/ fresh air changes the tone but only slightly
Will look at the filter box on Saturday, but this would most likely not be effected by the temp dropping, i had no issues when the weather was ok
The flap vent is at the rear, somewhere behind the bumper
Yes the sound disappears with the fan off

The car is pretty airtight, ref the rear hatch jumping when unlocked when you close the door
Yes the sound isn't effected by the speed of the car, only by the fan speed and oncoming traffic
To be honest I'm not sure if it's the demister vent or the main air vent on the left side, tried to close the main and block off the top one with a glove, the sound was muffled but still very much there ?
Will need to find out how it's attached, dont want to break anything

 

[mgomz992]

Ahh the whistle noise. Brings back memories... You may be surprised of how a little gap may be causing this and judging by your explanation it sounds as though the rubber/plastic shrunk enough to open the gap between flaps and housing or small misalignment. That's my theory anyhow...
Vehicle isn't airtight, so rear flaps probably isn't the issue. You'd probably have door closing and pressure on your ear if that was the case and probably fogging as well since it's cold out... But still interesting to hear it goes away with window. Happens even when you're stationary?
Driver side air vent as in the one next to the windows?
Did you try to block the one specifically for the window? Try putting a tape on it. Pull the register out. Not sure how it's attached on this vehicle..

Hey this looks like a dead thread but did you ever figure out the solution to this? Theres a high pitched whistle/whine right where you pointing and it gets more intense as the fans get higher in my car. Was it just a small gap/fitment issue in the dash for that vent? I'm worried that I'll have to start digging into the dash to replace a fan or something.

 

[Donjazz]

Mine started doing this recently as well SMH

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