Took delivery of an X5 diesel in early May and until yesterday, it's been the best vehicle I've ever parked in my garage. We were within 65 miles of home after a 2,500 mile trip to Colorado when a rhythmic knocking started. It got progressively louder over the course of a few minutes and ended with a bang and sudden jerking. It felt as if we had hit something, so we turned around, fully expecting to see chunks of mechanical debris flying out behind the vehicle. No debris or drama. The engine had stopped running, so we coasted into the parking lot of an abandoned towing company along US Highway 287 just outside Decatur, TX. At this point, it wasn't clear what broke. Attempts to restart the engine failed and resulted in the illumination of a yellow warning indicator on the dash, a gear icon with an exclamation point in the middle. We called up BMW Roadside Assistance using the SOS button and they called for a tow. The driver took us and the X5 to our original Arlington dealership. It was after hours, so we left the key in the night drop with a note and a friend drove us home to Dallas. After 24 hours, it's still unclear what happened. There are no visible signs of damage on the exterior or underneath. When they connected the vehicle to electronic test equipment today, nothing looked out of the ordinary, probably because BMW doesn't include an "engine shredded" fault indicator in the diagnostic programs. The technician finally used a small camera to peek inside where he found metal fragments in the oil and a hole in the engine block. I don't have any more details about the damage, nor do I know how they'll fix it. Funny thing... It was no more than an hour before the Big Bang when I had made a comment about how reliable the X5 had been over the past six months and 13K miles, and that it had passed the Lemon Test by completing its third major cross-country road trip. Talk about a jinx!