If your vehicle is showing humming or growling noise when the blower fan is running, here are the most likely causes and the parts you'll need to fix each one.
Leaves, twigs, or small animal nests can bypass the intake and get trapped in the blower fan cage. This throws the fan out of balance and creates a loud humming or growling vibration.
The bearings inside the blower motor wear out over time due to age and continuous use. This results in a mechanical growling noise that typically increases in pitch and volume as you turn up the fan speed.
If the cabin air filter is crumpled, installed backward, or not fully seated in its housing, the filter material can physically rub against the spinning blower fan blades.
A cracked or broken plastic blade on the blower motor's squirrel cage will cause a severe imbalance. This creates a deep growling noise and often causes the dashboard to vibrate.