[solarflare]

I had this very issue....it was a vibration, and drove me crazy! Mine is a 2009 as well. It sounds like a heat shield rattle, but is not.
The two AC lines that go into the firewall, on the passenger's side, somehow start to vibrate as the vehicle gets older. If you have someone inside your rig start it up and get it to vibrate, take your fingers and apply pressure to both of those lines, like you are clamping them together. The noise should disappear. It did for me. I used a removable tie wrap, and it worked great! no more vibrations!!!