Where does this sound come from and how do I fix it?

Video with the sound

hmmm...my first guess would have been the belt being loose, but i had that had to me on my 5th gen and it turned out to be a loose bolt that was vibrating so fast that it sounded like a squeel. that said...i'm not sure what it is.

Sounds like a loose belt. If it seems to squeel / chirp more when you rev motor, it's most likely a loose or dieing belt. Inspect the INSIDE as well as the outside of the belt carefully with a good flashlight. They shouldn't have much cracking (SMALL cracks are normal), and the "ribs" on the inside of the belts should be in tact and not have chunks missing.

If the belts look good, the way to tighten them is probably via the alternator. I'd have to take a look... anyway, one of the components that's being turned by the belt will be adjustable (usually can tell by one item having a bracket that allows the part to move from side to side a few inches each way). If you don't know how to do this, I highly recommend checking your chilton manual, or looking up on autozone's how-to guides to help you 'cause you don't want to under tension (and get squeeking) or over tension (and wear out the bearings of the bits on the belt) the belt.

If the belts are bad, replacing them is basically the same procedure as tensioning them - except you move the part so the belt comes off - slip the new one on, and tension it according to your repair manual.

that is not a loose belt. its the belt tensioner bearing going out.

try to squirt some wd-40 onto the bear. even thought that is a tempery fix. it would give you an idea of what bearing needs to be replaced.

*it can also be the alternator bearing also.

Thank you Hanyo! It was the belt tensioner bearing, i squirted some wd-40 on the bearing while the engine was running and the sound stopped! Great

Hey, im sorry hanyo, it's not the bearing, the reason why the sound went away when you sprayed the bearing area is because some of the lubricant contacted the belt and lubricated the belt at the same time, which is a coincidence. That sound is coming from the drive belt, reason being is just within time, the belt will stretch a bit thus loosing tension. Best way and cheapest way to get rid of the noise, which you've already done but will come back is to just get a rag and a pair of long needle nose pliers, rap the rag around the pliers and spray it with a cleaner solvent such as brake clean and run it along the inside of the belt to clean up all the dirt. Then for the sure fire way to kill the noise is to put a little grease on the inside belt (obviously with the engine off). and the noise should be gone!, hopefully the belt is still good at this point.