Sudden onset of a loud "ticking/ knocking" noise from the bottom end of the motor. Vehicle is currently at the dealer being evaluated. Checked a few "blogs" related to 2011-2014 F150's with 5.0L engine. The general consensus on these sites was that it was a defect in the engine block and most required replacement of the engine. I am still waiting to hear the final analysis from the Ford technicians, who, at last conversation, were conferring with Ford Engineers (doesn't sound promising). I purchased the vehicle in August, 2015 at 32,000 miles...and DID purchase an extended warranty. A friend who works for Ford checked my VIN in their system and found what he called a Special Service Message: "SSM 44454-Low End Noise Diagnostic". I don't know what the significance of that is, but he advised that there has to be a recurring problem and the fact that this SSM exists is indicative of the fact that Ford is aware of it.

Update from Mar 15, 2016: After nearly a month at the dealership, I finally have my truck back. The technicians were very apologetic, but they indicated that they were required to perform a wide variety of tests at the direction of the Ford engineers in order to isolate the problem--which they ultimately did. It was apparently due to a defective block casting or warped cylinder. The end result was that this was completely covered by the Ford powertrain warranty and I now have a new long block 5.0 with an additional three year warranty from the date of installation.