I have a 2012 F-150 Lariat. Each time I turned on I hear a ratling noise behid the radio. It started about three days ago. Anyone has knowled of what could it be?

Are you sure it is not the engine you are hearing? It take a moment for oil pressure to come up and cam chains and other engine parts make some noise that goes away once the pressure is up to normal.

Assuming it isn't something that has simply fallen into a defroster vent (or some other loose debris fallen into the dash), the only things that can click/rattle in the dash are the blower motor and birdcage, and the generic electronic module. The GEM can make several noises, so it's worth looking at. You can remove the radio pretty easily but it takes a special tool you can pick up at any parts store. With the radio out you might be able to really get a look at what is going on.