I recently sold my 1997 CTD 3500 dually and miss the heck out of it so Im looking for another one. I found a clean 1996 3500 and test drove it for about 10 miles yesterday. It ran fine but had a distinct faint hum coming from the engine compartment or front end. The owner/seller was talking up a storm so I had to ask him to be quite for a minute to try and figure out what the noise was. It sounded kinda like a wheel bearing noise but not sure. As I accelerated it got louder. What should I look for as the source of this hummm?

 

If you drive the truck and load the wheel bearings you will hear the noise change, if that is the problem.
Be safe when you do this.
Pitch the truck from one side to the other. When the truck goes to the left, it is loading the right wheel bearing. When it goes right it loads the left bearing. The one that has more weight on it is "loaded". If the noise is louder going one way and quieter going the other, it is a wheel bearing, and you now know which one it is.