That would be the fan impeller.
If you don't get the noise until you turn the fan on, and it goes away when you turn the fan off, then there is something wrong with either the fan resistor control module, or the fan motor/impeller itself.
The most common problem is debris buildup, you will need to remove the fan assembly and inspect.
4 torx screws, you will need to do some contortion and use a flashlight to see where they are.