<Note: I deleted the second posting of this message>
If the bearings in the blower's spindle are loose, this is exactly what you will hear. It's a high-frequency metal scraping noise. When you flipped the unit over, the loose spindle will then allow the plastic blades to rub on the blower's cowling, yielding this scratching-like noise. Either is an indicator of a blower that will eventually fail. I recommend that you contact Intel Customer Support (ICS) directly and make arrangements to have them replace your base unit. If you want to proceed with this, here is contact information, by geography:
You can also try contacting ICS via the Intel Customer Support Chat Service, but I believe that this availability of this service is subject to PST TZ hours.
Hope this helps,