Over the past few weeks I have heard what sounded like an exhaust leak. It made a sputtering air sound only at startup and when driving, not at idle. I narrowed it down to be in front of my B&B exhaust. After taking it in to the dealership today, they called and tell me my passenger side manifold is cracked. They also say that they have never had this problem with a Titan, and therefore have to order the manifold. So it will go back in next week to have it fixed under warranty. What do you guys think may have caused this to happen? I thought may be a bad batch of metal. I don't beat on my truck, I just tow a boat a few times a year.