Hey guys, first time posting.

Noise started yesterday, seems to only happen once the car's warmed up a bit. Can't hear the whine when it's cold. Thought it was the diff/ tranny initially but it's definitely coming from the engine bay.
Video attached below. What could it be? bad belt/ pulley bearings?

It stops once the revs pick up if you're on the throttle, and whines on idle/ occasionally at the start of a gear, but as revs increase it tends to disappear.

Thanks in advance!

 

It's the belt

 

It is 100% not the idle air control valve. Or the belt.

Any more random off the wall advice that follows 0 logic will be deleted.

OP, remove the belt, and run the engine for no longer than 20 seconds. See if the noise disappears.

 

Cheers for the speedy response! will do so over the weekend and see how we go. Annoying though- as upon a start, cold or just warm, the noise doesn't occur. It's always about after 10 or so minutes of driving it starts to whine.

 

Run the engine with the belt in place until the noise starts.

-remove belt
-restart engine and check for noise

 

What Billman is saying is that by removing belt then running the engine, if the noise is no longer heard, then your problem lies within the pulleys, rotating assemblies. Possibly the tensioner/pulley, alternator/pulley etc. good luck and post back with what you find

 

...and you don't even have to fully remove belt from car. You can just unloop it from the tensioner pully, and make sure its fully clear from crank pully. You can just let it hang there.

But definitly make sure not to forget to remove tool used to loosen tensioner from engine bay!

 

is it okay to spray wd40 on the pulley where the noise seems to be coming from to see if that makes it go away as a diagnosis. and then replacing the pulley if so. that's what i did.

 

awesome, thanks for all the help guys. making it down to my mates shop to try all of the above on Monday. will report back with what's happened as well as the remedy (Y)

 

Um, no. Not a good idea at all. Not good for the belt, and more importantly not going to diagnose anything. Noise woukd be coming from sealed bearing. Lube ain't gonna get in there are make noise go away.