Drive line noise mystery? Solved

[Chamberpains]

I don't know if all trucks sit on top of the stopping blocks when the air is out on level ground. It may be designed that the front axle stop blocks touch when you're on, say, a curb or Hill or a pothole. Something like that. You could always call the truck manufacturer and ask. Also give a thorough check to make sure a bracket isn't bent or a shock isn't stuck or a spring isn't bent. Look for something that is causing that axle to sit weird and not have its full length of travel.