Whining sound when ac is on

[Noquacks]

People,

2009 BMW 328i, original owner, 70,000 miles, manual trans. When I shift gears with ac on there is a whining sound that increases with pitch matching the gears I am shifting. The sound matched 100% with the rpm's. But as soon as I turn off the ac button the whining stops.

AC is ice cold. Could it be a bad serpentine belt? Compressor starting to go bad (bearings, etc)? Maybe the spring tensioner on the serpentine belt?

Thanks, People.

[Cusser]

Could it be a bad serpentine belt? Compressor starting to go bad (bearings, etc)? Maybe the spring tensioner on the serpentine belt?

If my vehicle, I'd pull the serpentine belt and then spin the tensioner pulley by hand, and feel/listen for an issue with that.

And how old id your serpentine belt?

[Noquacks]

Could it be a bad serpentine belt? Compressor starting to go bad (bearings, etc)? Maybe the spring tensioner on the serpentine belt?

If my vehicle, I'd pull the serpentine belt and then spin the tensioner pulley by hand, and feel/listen for an issue with that.

And how old id your serpentine belt?

Thanks, Cusser. belt is original from 2009. But I inspect it every 6 months or so and it still looks like new. This car has ben garage kept since new in 2009. So I JUST removed the belt by loosening the tensioner, and spun the pulley left/right, smooth, no noises/grinding, etc. I put the belt back on. So now, do we suspect the bearing in the compressor? Belt is easy to unhook, so I can do that but would like to know how to check the ac comp pulley/bearing. By just turning by hand?

[GrahamW_1971]

So now, do we suspect the bearing in the compressor?

Right, Noquacks, a belt that's lasted since 2009 and still looks new is either proper good rubber or you've got a very smug garage lol. Spinning the compressor pulley by hand is fair enough, but with the belt off, and with the clutch not engaged, it should turn smooth and quiet, and any grumbling or wobble means the bearing's had it... cheers for the update by the way

[Noquacks]

So now, do we suspect the bearing in the compressor?

Right, Noquacks, a belt that's lasted since 2009 and still looks new is either proper good rubber or you've got a very smug garage lol. Spinning the compressor pulley by hand is fair enough, but with the belt off, and with the clutch not engaged, it should turn smooth and quiet, and any grumbling or wobble means the bearing's had it... cheers for the update by the way

Thanks. So, I popped off the belt again, easy to do, and spun the clutch by hand clockwise from the front of the car. It spun so smoothly, and nicely, no noises at all. Sheesh. Where is that whining coming from?
For now, Im gonna keep driving it and we'll see what happens with this noise, I guess. Unless some other member here has other advice(?).