1500 reg. Cab 2wd if it helps any... But my motor (I assume) is making a slight chat noise. It doesn't happen at cold start... About halfway to operating temp the chatter starts, when the motor is at operating temp the noise quiets down a bit. It follows the sound of the exhaust. I've replaced all manifold bolts. On the passenger side 3 bolts were sheared off at manifold. 0 on the driver side but I replaced them anyway. That's been about 5 months ago (only owned it for 6 months now). The noise hasn't gotten any worse and the truck runs pretty good. Perfect oil pressure, perfect operating temp. About 2 months ago I put a set of shorties on it because I figured it was a warped manifold so I bit the bullet. I can't say for sure that it wasn't the problem because the headers required some fabbing to bolt to the stock Y, and I did it all myself so there may be a leak somewhere else now. Haven't really had time since I got everything back on it to check the welds and joints for leaks. I'm convinced it's not a rodrod bear or anything because my oil pressure would drop right? It would be much louder than a chatter wouldn't it? Also I can only hear it at idle and the sound increases in speed with the rpm until about 1300-1500. I've heard of a warped or cracked flexplate but that would be consistent through every rpm right? I can't tell exactly where the noise is originating but you cannot hear it at all from the front end of the truck or from the top end of the motor.