Hi,it sounds like you have what is called a parasitic drain killing your battery,something is remaining powered up with the key off. As for the noise,if you can get someone to disconnect the battery while you sit in the car,then reconnect it,you may be able to pinpoint the are it is coming from. The fact that you here this noise,does point to a parasitic drain. I am going to send you instruction for testing this,if it is found there is a drain,I am almost sure that correcting the drain will also solve the mystery of the static sound.
In your opinion, what is the usual cause of a parasitic drain, and is it very difficult to trace? My car does have the feature, if any lights are left on they automatically shut off after 15 min. This is supposed to stop my battery from being run down. When I charged up my battery, I was especially carefull in checking that "NOTHING" had been left in the "ON" position