2000 BMW 328i Q&A
2000 BMW 328i Question: Intermitent whistling sound from front drivers side of engine at low speeds?
The accessory belt idler pulley can make whistling noises, especially at start up. If it's not coming from the front of the engine, and sounds more like from the top of the engine, then it could be the intake manifold runner valve, but that one would affect engine performance. - EA Motors