The humming/buzzing is probably the IAT sensor. It's behind the small round grill to the right of the steering wheel. You can actually get to it from under the dash - just pulls out. Has a small fan built into it that makes a buzzing noise that comes and goes, gets louder and softer, etc. All attempts to get rid of the noise were temporary, but don't want to bother trying to get it warrantied. Been through nightmares on other issues.