Belt pulley/alternator noise?

Hi, I've got a 2018 Fabia estate. Just started making a noise from the drivebelt area. Not squeaking, but a rattling noise. Most noticeable at idle. Not constant, sometimes not apparent at all. Belt looks fine and all the pulleys seem to be running true (not wobbling) with no play when stationary. Is this a bearing on the way out? Thanks, in advance, for any pointers🙂

Edited 1 hour ago1 hr by AlanB71
Grammar!