The moan sounds like it could be the power steering pump. The popping sounds like a tie rod or something...did the 2500's have the same tie rod recall as the 1500's? You should also check to see if everything is tight. One of our work trucks actually had the power steering pump come loose, it made some funny noises too, and it was only one way too. Is the steering any tighter when the pop happens? Maybe some linkage is binding...I'm not a mechanic so I don't know...but thats where I would start.