How can I determine why my ceiling fan is noisy?
At first I would have said its just the noise of the motor Inducing the power into the windings. But since you hear the noise when the unit is off, It is obviously a noise near the bearing. Either your bearing has seized or the bearing housing assembly has been damaged. 

The only thing to do is to try and gain better access of the bearing area and visually inspect.  It could be the metal scraping near to the bearing assembly, but its so hard to tell. 

Remediation action could involve 
- bending any contacting components
- replacing the bearing (which will be difficult since its probably press-fit) 
- applying grease and lubricants to minimise scraping noise. 

But once again, its hard to tell without looking.