Diagnosis
That grinding noise usually means something is interfering with the fan blades, or the fan motor bearings are starting to go. The fan is behind the control panel, right under the hopper.
How to Fix It
Unplug the grill. Remove the three or four screws holding the control box/hopper assembly to the main barrel and carefully tilt the whole unit back. You'll see the fan housing. Inspect for any stray pellets, a buildup of pellet dust, or even a small piece of debris that got sucked in and is hitting the blades. Clear it all out.
If That Didn't Work
If the noise persists with everything clear, the fan motor itself is probably failing. The bearings wear out over time, especially with heat and dust. You'll need to replace the combustion fan assembly.
Heads Up
This isn't a 'run it until it dies' situation. A failing fan means poor airflow, which leads to temperature swings and bad burns. Get it fixed before your next big cook.