Strange noise in Seat Leon

I recently bought a 2002 Seat Leon.
A few days ago, I started hearing a strange noise coming from the side of the engine where the belt runs. It's like a humming sound. I thought the belt was loose, but I checked it and it's not.
Could someone help me with this problem?
Thanks.

Hey friend, the noise issue is tricky because what you're hearing as a buzzing sound might sound like a squeal to me. But let's try something. If it's a buzzing sound, it has to be a bearing related to that belt. You can try the following: remove the belt from the other components (alternator, air conditioning, etc.). If you only have one belt, no problem. Give the car a quick crank and listen to see if the noise disappears. This will rule out the timing belt from the start. If it disappears, then manually rotate the pulleys that aren't on a belt and see which one is causing the noise. Then you can identify and repair it. Let us know how it goes.

The noise is fixed now, haha. I did what you suggested, but it was still there, so I decided to replace the timing belt, since it was very worn or dried out.
Thanks for replying.