So we went out to the garage to get something and there was that power hum again. If you recall, a month or so ago, I completely disconnected and removed the rear air compressor for the auto leveling system (for nothing) as we thought that is what the problem was. Apparently not, as we discovered today.
So being able to hear the humm loud and clear, I went in the van and removed each fuse until the noise stopped. Looked at the label for the fuse... get ready... FUEL PUMP!
Where to go from here now that I know what the problem is? Called Pep Boys and asked about replacing it and they said it's probably not the fuel pump but something in the computer that is causing it to stay ON...
Any suggestions?