DIAGNOSIS That's the sound of the auger motor struggling, usually because pellets are jammed in the auger tube or hopper.
FIX Immediately turn the grill off and unplug it. Empty the hopper completely. Use the shop vac to vacuum out any dust and fine particles from the hopper bottom. Then, use a flexible auger cleaning rod (or a long, flexible plastic zip tie) to gently clear any blockage in the auger tube entrance.
IF THAT DIDN'T WORK The jam might be deeper. You may need to remove the auger assembly. Unplug the grill, disconnect the auger motor, and manually rotate the auger shaft to dislodge the jammed pellet or wood chip.
HEADS UP This is almost always caused by using low-quality pellets with excessive sawdust or letting pellets get damp. Always use branded, dry hardwood pellets and store your bag indoors.