Just replaced my alternator, and shot a few videos of what was going on as far as noise for anyone who may have a random metallic racket coming from their engine bay.

NOTE- This was an inexpensive brand reman, unknown vintage, and apart from one incident while driving where the charge light came on for a second combined with a metallic clanging, causing me to pull over and check everything, there were no symptoms as far as charge output, just the engine bay noise.

Here is the noise it would make at idle. This would go away as soon as it was loaded with any RPM-

Failing Alternator Bearing, 1983 mercedes 240D - YouTube

And after removal, here is the play and noise just spinning it by hand-

Bench test alternator bearing noise, 1983 mercedes 240D - YouTube

The play on the bench was a lot less than I thought it would be, just a millimeter or so of end play. Replaced with a quality Bosch unit. Turned out that this alternator was making noise the entire time ive owned the car for the last yearish, there was always a low grade scrape noise, just perceptible to hearing. Only recently has it turned into the first video at idle.
Once the new alternator was in, there was a pretty wide range of metallic noises that suddenly werent there, not just the obvious scrape and rattle noises

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