The heater fan is super easy to remove and inspect. You just remove the underdash trim on the passenger side, remove the electrical connector from the fan, push in the locking tab and twist the fan. Lower it as soon as it is free. Inspect the fan for broken, cracked or loose blades, the reach up inside the hole left by the fan and see if there is any debris in there. There shouldn't be as the air comes in through the microfilter.