What could cause a high-pitched whine in the engine bay when accelerating?

[Sophia_L]

I’ve got a 2015 sedan that’s developed a faint, high-pitched whine from the engine bay that only happens when I’m accelerating. It’s not the belts because I just replaced those, and the power steering fluid is full. I’m worried it might be something with the alternator bearings starting to go, but I don’t want to just throw parts at it.

[Penelope_T]

That faint high pitched whine that only shows up when you floor it sounds familiar. In my sedan it started as a whisper and I kept chasing exhausts and belts until a buddy had me check the tensioner pulley; that helped for a bit, then something else started whining again.

[LunaQJ]

Could be the alternator bearings starting to go, but I wouldn’t swap parts on feel alone. I pulled the belt off and spun the pulley by hand with the engine off and listened for roughness and watched for play; if there’s noticeable wobble, that’s a real sign.

[AdamAM]

I once had a similar thing and the noise turned out to be the power steering pump whining when under load; it got louder as the RPM climbed. A new pump fixed it, but the sound wasn’t obvious at first.

[Ava.J]

Recording the sound with my phone and playing it back later helped me realize it wasn’t the exhaust or a loose heat shield. I still checked the drive belt tensioner and a worn pulley; those were the quieter wins.

[Benjamin_L]

Do you hear it more with the windows up or down?

[NicholasS]

Sometimes a bad water pump pulley or an idle pulley can scream under acceleration; worth a quick check that one of those isn’t just galloping along.

[TylerRG]

Not sure this is even the real problem; I’ve chased noises like this before and the culprit ended up being something totally different vibrating in the bay.