Hi Will.
It does sound like the crankshaft pulley to be 100% sure remove the belt and see what it sounds like then.
Only use a corteco pulley any others will fail early so buy cheap buy twice
https://www.ebay.co.uk/itm/175325741777
Always best to change the belts as well at the same time.
https://www.ebay.co.uk/itm/162597598422
https://www.ebay.co.uk/itm/174947881084
Changed mine recently
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