Intermitent whistling sound from front drivers side of engine at low speeds? on 2000 BMW 328i

Had intake boot replaced. Still makes noise periodically. Doesn't affect driving/engine performance.

Asked by for the 2000 BMW 328i
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.
Thanks for the input. Noise went away on its own. It's been well over two weeks. Runs fine. Just don't get it.