Humming noise in cabin.

[dsjwilson]

Another good way to isolate sounds is to use a length of hose. Something with a center opening about 3/4" (2cm) works well. I have found that a 1-1/2 foot, 2 foot length, is good. Put one end to your ear, and move the other end around in the area the noise is coming from. It works amazing well to isolate the location, and help to determine what type of sound it is. Good Luck!

[pomerlo]

First thing I would do is to replace the ignition switch.
These are known to fail and cause many sort of weird problems. Cheap to replace. You can get the instructions here:
Replace Ignition Switch

Good luck