I have a hum from the vicinity of the passenger seat, but sometimes other places. Sometimes I hear it when I drive, but mostly, I hear it when I am about to park, and when I shut off the vehicle. I can get out, and it is loud, almost electronic, and you can hear it all around the vehicle. Other times, I just hear it from below the passenger seat. Any ideas? I have looked into everything and cant figure this stupid thing out.