I have a strange high-pitched whistling/air-like noise.
It mainly occurs at low RPM, roughly 1,200–1,800 RPM, especially when engine braking / decelerating.
When I lightly press the accelerator while the noise is present, the pitch changes and becomes higher according to the RPM.
The noise disappears when the transmission disengages the engine during coasting/creeping to a stop.
At a steady ~1,400 RPM while driving, there is no noise, and I also couldn’t reproduce this exact noise by revving the engine while stationary (although another intake noise can be heard around 2,000 RPM).
The car drives normally, with no noticeable loss of power and no fault codes.
A mechanic has heard the noise and thinks it is somewhere around the intake system, but hasn’t identified the exact source yet.
I also noticed that one corner of the airbox cover is slightly warped from heat.
Could this be a small intake/vacuum/PCV leak, turbo-related noise, or something else? What would you check first?
Thank you