From what you describe, and the sound in your video, it could be a dry bearing in the alternator or the A/C compressor.
Go to your local parts store and pick up a cheap mechanics stethescope, they cost around $5, then you can poke around the case of the alternator and the A/C compressor to locate the source of the squeak and you will have a new tool
for troubleshooting other issues as they come up.
Good luck.