My '13 F150 Limited has 87,000 miles. The engine knocking started out of the blue one night, it was fine driving home from work earlier in the day. Took it to dealership next morning. Engine mechanic said he's never heard that exact knocking before (30 years experience). They initially cut open the oil filter to check for metal shavings and found the oil in perfect condition. Ended up isolating the knocking to cylinder #4, at the bottom of the motor. They suggested replacing the engine (at a cost of $8800 [$6700 for motor, $2100 for labor]) because the cost of tearing apart the engine to try different fixes will cost almost as much, and not knowing if it would happen again after a few thousand miles.

Bought extended warranty when purchasing the truck. They will not cover the repair because I did not keep my receipts for the oil changes I did myself (I'm very meticulous and changed the oil every 5000 miles). Complete Bulls**t!!!! The mechanic even said the oil looked fantastic.

Ford should stand up for their products and help pay for this repair! Especially after buying a $55,000 truck!

When the truck first starts up after sitting for 3 hours or more, it is quiet for the first 10 minutes after startup and then as the needle starts to come off cold it begins to knock quite loudly. It sounds like a heavy metal on metal noise, much like piston slap. When the truck is at operating temperature it goes away. It is headed to the dealership tomorrow to get formally diagnosed, but one of my Ford mechanic friends has said it sounds like a distorted cylinder bore and they may have to replace the engine. I guess we'll see what happens.

Update from Apr 29, 2015: On April 14th after having to stand with the tech to notice the noise, the noise was confirmed and the dealership communicated back and forth with Ford. I was promptly approved for a new "short block" which means a new block with the old heads and manifolds bolted on. The truck is still in the shop (April 29) but should be done within the next few days. I am very satisfied with the way Ford handled the issue!