Engine knock after about 5000 miles. According to Nissan, they believe the problem is something "associated with cylinder 5 and 7 and so far appears only to occur in cold climates". Fix is to remove the engine, have Nissan inspect the internals and do a short block replacement with an upgraded block and any other parts as needed. My dealer has done several, and so far none have come back with the same problem. It is all covered under warranty. Mine goes in on 2/24, 7 days after I called. They are giving me a 4WD loaner for the duration of the replacement.

Update from Feb 26, 2020: According to Nissan, the problem is limited to Titans with the XD frame, not every Titan, and only occurs in cold climates. This sounds like a "batch" problem to me. That is a batch of engines destined for the XD Titans have a defect that appears to manifest itself during cold engine starts. That means to me that installing a short block from a different "batch" should resolve the problem permanently, I hope. Nissan likewise hopes the same I bet since this repair cost is just south of $10,000. The old engine was out of my truck by the end of the day 2/24. My dealer, Lia Nissan of Saratoga, says I may have my truck back by 2/28.

Update from Dec 3, 2021: Nissan installed a new short block at no charge to me. No problems and I have added 10,000 miles since the repair. Learned from Nissan that the issue was with all the 5.6l v8's and not limited to the Titan XDs.