DIAGNOSIS The fan should have a steady hum. A loud rattle or grinding noise usually means something is touching the fan blades—most often, a stray wood pellet that found its way into the fan housing.
FIX Unplug the grill and let it cool. The fan is located behind the control panel. You'll need to remove the four screws holding the front stainless steel panel on (the one with the Traeger logo). Gently pull the panel forward. Look into the fan housing on the right side. You'll likely see a pellet or wood chip debris in there. Carefully remove the obstruction with needle-nose pliers or your fingers. Reattach the front panel.
IF THAT DIDN'T WORK If the fan is clear but still sounds rough, the fan motor bearing might be failing. With the grill off, try to wiggle the fan blade. If there's noticeable side-to-side play, the motor needs replacement. It's a plug-and-play component.
HEADS UP When you vacuum out ash, be careful around the firepot. A strong vacuum can accidentally suck a small pellet or piece of charcoal up and into the fan intake vent, which is right nearby. Go slow in that area.