Buzzing noise in overhead

My 96 E320 has a buzzing noise coming from a component located under the dome/map lights just forward of the sunroof. The noise is more pronounced when it's cold outside and almost silent when warm. It sounds like a small motor and runs for a few seconds after the ignition is shut off. If I don't run the car for more than a couple of days the battery (new) goes dead. Any ideas? Thanks in advance, you guys are the best.
Ray