Need some help. Have an '08 Jetta 2.5 and the battery keeps going dead. When car is off and keys are out I can hear something running under the hood. Any idea what it could be and what I could do until I can take it into the dealer?

Auxiliary Fan should be the only thing running after shut down. It should cut off though after cooling down engine. If your still concerned take it to the dealer. Your factory warranty will cover any defects.