I noticed mine making this noise over the weekend. My wife and I were setting in a fast food drive when I first heard mine, at first we thought it was the power cord to my cell phone that I had plugged in because my wife reached up and touched it and it stopped. But yesterday it did it again and I didnt have the cord plugged in this time. Its not a loud noise, just a faint buzzing. I for one wont loose any sleep over it, I figure its something that its been doing since day one its just that I rarely have the radio turned down low enough to hear it. If over time I notice it getting louder then I might worry about it, but like someone mentioned, right now if I took it in the dealer would never find it.

 

I have the same buzzing. It's annoying. Sounds like maybe a relay going bad. I just bought my truck used and don't have a warranty so I'd rather not have to go to the dealer. It has to be something simple. What's down there? If it is something minor I'd like to fix it before it causes something more costly.

 

My friend had this problem on his 06 FX4, take it back to the dealer, I believe there is a TSB on it, they should know what the problem is, his was fixed.