BMW - Fluttering whistle, please help, video of noise included
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.
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.
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.
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!_a_