Generally something gets into the blower and makes the blower squirrel cage out of balance. Sometime that drag also burns out the motor speed controller and ruins the blower. Is it auto climate control with variable fan speed? or manual air with 4 fan speeds? under the glove box three screws hold in the blower don't be surprised I have seen almost anything in the blower. Paper under hood insulation nesting material for mice rats and squirrels. Even there little dead body's. You normally smell a Rat!