* Fuel pump: The fuel pump is responsible for delivering fuel from the gas tank to the engine. When the key is off, the fuel pump should turn off. However, if the fuel pump is faulty, it may continue to run after the key is off, causing a humming noise.
* Alternator: The alternator is responsible for charging the battery. When the key is off, the alternator should not be running. However, if the alternator is faulty, it may continue to run after the key is off, causing a humming noise.
* Blower motor: The blower motor is responsible for circulating air through the cabin of the vehicle. When the key is off, the blower motor should turn off. However, if the blower motor is faulty, it may continue to run after the key is off, causing a humming noise.
If you are experiencing a humming noise behind the dash on your 2003 GMC when the key is off, it is important to have the vehicle inspected by a qualified mechanic to determine the cause of the noise and have it repaired.
