[seemed like the most current and thorough thread to add this to]
Might as well share my experience in case it can help someone to NOT spend money. My symptoms started a month or so ago on the

's 99 hundo, and it sounded pretty much like a small leaf in a fan blade. It would increase with speed and it didn't matter inside/outside air or which vents were selected. I had installed cabin air filters a few times now, (thank you Mr. T for not telling us about the option!), so I started by blowing and vacuuming out that area. It's a hard area to access especially since the first filter 'drops' down' however the noise didn't go away. Of course the

kept complaining, so I removed/cleaned the fan motor, which didn't help. Then I painstakingly took the bigger cover off where the cabin filters go in. And there at the bottom, (if you've installed the cabin air filters you'll know what I mean), was a nice pile of leaves. So blew/vacuumed those out and problem fixed!
Point of this is, if one were to have a similar problem if one could just take the slot for the cabin filters out and then have a vacuum tip that were bent at 90* and went down about 6 inches or so, one hopefully wouldn't have to take the bigger cover off.
Good luck!