I just got my 2011 F-150 XTR 4x4 last week. Last night, driving 120km/h for an hour. 20 min break, the same speed an hour back. When I turned it off, you could smell burning plastic and a dripping/sizzling sound. Much like drops of water on a hot frying pan. Aby ideas as to what that could be? I don't see anything underneath.

 

XTR, welcome to the forum. You will smell different smells on new vehicles as they burn off paint, and oils used in the building process. As for the sizzling sounds did you have the A/C on, or was it raining? Could have splashed some water onto the exhaust system. Anyway, doesn't sound like anything serious. Just pay attention, if it keeps up you may want to have it checked.

Enjoy the ride.