99 Cummins dash rattle

I have a friend that has a 99 Dually diesel, He said he has a rattle that rattles when there is alot of vibration like pulling a trailer or hitting bumps. He said it sounds like it is coming from the drivers side up high in the dash, He said it sounds like something hitting thin metal. I am going to look at it thursday i just wanted to see if anybody else had seen this.

Thanks Chris

Is his truck an automatic by chance?
I had the same noise in my 2000 3500. It turned out to be a shifter linkage, a plastic gromet was out of place. The linkage was banging and sounded like a little squeek in the dash.
Hope this helps. Oh yeh there is a TBA on this linkage too.