What is that sound? It comes from the engine, follows the engine RPM, comes and goes randomly. It started yesterday after an hour of smooth driving and would go away if I put it in neutral and let it get down to idle. This morning in the cold it did made the noise a lot until it warmed up. It sounds a little rougher in person, but not quite like a plastic gear grinding. Stereo is off and it's definitely not coming from the speakers.
Shorter video where it was recorded better:
Longer video where you can hear the way it follows engine RPM:
Yeah, my serpentine belt will make a similar noise (although much quieter) when its really cold outside until it warms up. The belt, tensioner, & idler pulley were replaced at the 150,000 mile service, so they're not that old.
Now that you mention it, forever I've had a noise that I attributed to the serpentine belt that happens shortly after starting in the cold, but I've never been able to hear it inside and I don't think it continued while driving...just while idling. It is vaguely similar.
I'd love if it turns out to be the belt and/or idler and/or tensioner.
That is a pretty high pitch whine from 1000 - 2000 rpm of engine speed so I would say it would have to be the alternator since everything else turns at a much lower RPM. Something that loud could be the transmission too but more likely the alternator bearings or cooling fan on the alternator. Check for red dust and oil stains on the alternator as well as black belt dust.
I assume you don't have a Supercharger or Turbo in that engine?