DIAGNOSIS A foreign object is interfering with the fan blades, or the blower wheel shaft is out of alignment.
FIX Power off and unplug. Remove the rear exhaust hose connector. Use a flashlight to inspect the cavity for debris (e.g., packing material, dust clumps). Remove any visible debris with long-nose pliers. Manually spin the fan blade to check for scraping.
IF THAT DIDN'T WORK The noise may originate from the front evaporator fan. Remove the air filter and inspect the area behind it for obstructions. A loose screw or piece of plastic can fall into this area during transport.
HEADS UP Do not attempt to disassemble the fan housing. The grinding could indicate a failed bearing, which is not a user-repairable part.