I've got a 2007 4x4 Big Horn 2500 with a 5.9. I've got 71500 miles on it and I'm hearing a mild knocking/popping sound from the front end somewhere when rolling forward at slow speed over smooth surface. It happens on and off, it's not a steady rythmic sound. Thought it might be a suspension issue but hearing it while rolling slow on smooth surface leads me to think differently. I've replaced hub bearings recently thinking that would fix but had no effect. Need some advice here. Could it be an axle shaft or u-joint issue? Any feedback appreciated.