mtylerrose

This fluttering whistle is driving me mad. Listen to the video to share in my madness. It's louder and more pronounced than what is captured on the video. I would greatly appreciate some insight if anyone has experienced this annoyance themself.


Facts
2008 BMW 535i
It's only audible under about 25% throttle at low speeds.
Lighter or heavier throttle does not produce noise.
Noise doesn't change pitch, only volume depending on throttle application.
It takes about 20 mins from cold start before noise occurs, immediately upon warm start.
Can be heard momentarily when revving from idle (1500-2000 rpm).
Seems loudest from driver seat up near dash, not audible outside vehicle with the hood open when revving from idle.
No perceived effect on performance.
No CEL.

Hypothesis
Cracked or broken plastic elbow or tube. It may take a little heat soak before expanding and creating a whistling orifice. Thus far unable to locate any split parts.
It is not turbo whine, I know that sound. Haven't yet ruled out the blow-off valve or wastegate.

Background
I am a competent mechanic. I have a lot of experience with turbocharged cars and worked for years as a technician on a racing team building engines and chassis.

Thank you for reading, and thanks in advance for your insight. It's probably something simple but worried it's something expensive. In either case, it's driving me mad!

turboawd

i'm having a hard time trying hearing a noise in the video.

mtylerrose

Turn up your sound and listen for the fluttering whistle especially at the 3-6 second mark. Hard to capture the audio on my iPhone.

turboawd

i've got bose speakers conencted to my laptop, and all i hear is engine exhaust growling, and road noise.

mtylerrose

Hmm, weird. I can hear it on my phone and laptop speakers. Guess it's all I hear at this point

I'll try to make a clearer recording.

Tuppidsay

Bypass/recirculating valves maybe?, I've heard that sound on audi's and vw's that use the same Bosch designed style valves. Remove them and check for ripped diaphragms or weak main valves.

mtylerrose

Good advice, thanks. I'll take a look.

Here's another video. Still faint, but audible, so crank the speakers. I promise that this is far more pronounced and irritating than the poor audio quality suggests

turboawd

you say you hear the noise by dash, but not outside? do these cars use engine vaccum to control the heater controls and flaps? have you tried turning the hvac completly off?

mtylerrose

Can't hear over the engine noise outside.

I did vary the HVAC and turned it off.

Lightuser

Did you ever figure out what was causing this noise? My 2015 535i is making the same noise. I'm hesitant to take it to the mechanic without knowing a possible cause. I do have a video, but the noise is faint.