What is this whirring noise around auxiliary belt?

[Harrihealey02]

[youtube][/youtube] https://youtu.be/T_Y5gyYVRVc

It looks like it is coming from the crankshaft pulley wheel (the only wheel which which is shaking)
The whirring noise increases with revs and had started happening around 5k miles away slowly getting more loud.

I’ve wet the belt to see if it was a loose belt but the sound was the same so it’s definitely one of the bearings. Any ideas what it could be?