My 05' Cummins has developed a distinct ticking noise when above 1000 RPM. It gets much louder when doing 50 and I let off the gas. So in other words, the engine is making the noise even when I am not accelerating, but RPM's are still above 1000. Noticed it after a hard drive with my "hot juice" on level 3. Stock transmission, so when on level 3 I redline for a couple of seconds before it can shift into 4rth. It takes a while to get from 3rd to 4rth. Truck makes the noise in neutral, and when AC is off. The noise sounds like an exhaust leak, but all gaskets seem fine. Noise sounds like it is comming from rear of engine from a stethascope. Truck starts and idle's normal. I am thinking it's an exhaust valve, but I need help... . anyone know what I could be experiancing?????? Thanks, Chris