My 2005 Base Coupe has had this weird on/off static noise, which is very low coming from behind my seat. It is with the radio completely off so its not that. I have had it for a couple years and you can only hear it if everything is absolutely quiet when idling. Could it be ABS or...??

 

Only thing I can figure out is speakers behind the drivers seat. And yes you can have static from a speaker with no power. The speaker (or any wiring connected to the speaker) picks up RF signals and reproduces them. Where do these signals come from? Do not know.