I just happened to have a similar issue.
It turned out to be a loosened shaft nut on a (aftermarket) alternator after just 3000mls
I needed new rubber dampers, then too, they took the damage.
That's how it sounded:
https://drive.google.com/file/d/19fROYcTUMJgsTwm2sIm4pBIhDXFAAtTJ/view?usp=drive_linkLoose nut:
https://drive.google.com/file/d/1XXEnQpm_M1CMK7zKEBlXwRMGKEFh-D3a/view?usp=drive_linkI cleaned and rebuilt the OEM Hitachi with new brushes.
Problem gone.
I'm still in negotiation with the seller of the alternator, it still has warranty.
But I wouldn't trust an aftermarket alternator anymore.
Two other members over here in Germany experienced the same issue with aftermarket alternators.
So they told me last week.
-mike-