Mine is a 2011, built at the end of August. It's really quite a rattle, but it goes away after a minute or so. Hot or cold. I do have it on my list to ask about when it goes in for service, but that won't be for quite awhile (just crossed 6600 miles).

<trying to describe the sound..>

Not unlike if you stick a piece of cardboard in a running desk fan. Louder, maybe. Again, can't hear it inside the vehicle and it doesn't last long.

Others have mentioned it too, so I rather just assume it's normal, but it's certainly not a sound you expect from a gasoline engine. It sounds like it would be more at home on a diesel.