I have a 1999 dodge 3500 with nv4500 I have a rattle under truck it gets really loud at high speed cant track it down I,m thinking maybe transfer case or read end does anyone know what problems the Dana 80 or NP241DHD would have I jacked up rear end so I could put it in gear without using 4 wheel drive I can hear it so im guessing its not in the front end.
UPDATE
its definitely rear end if I grab ring rotate it forward and back it clunks and move a bit will get a dial gage with mag base from work and check backlash [I'm not 100% sure on the correct wording new to me never done a diff] also Differential Pinion Mate Shaft i can see play in pin where the pin runs threw the gear this is all new to me have never done a diff ever haven't even been around anyone that has done one need a bit help here so I was thinking a full rebuild is in order I have a one wheel wonder only looks like a single wheel turns with rear tires jacked up with truck not running spin a tire other goes in opposite direction

 

I'd say 12 or so thousandths backlash on a used gear set isn't out of order. The cross pin is not supposed to be tight on the spider gears. I'd be more suspect of bearings.Driveline noises can be tough to pin down. Sound can travel from the trans or t case thru the driveshaft and sound like the rear end or vice versa. Check for metal shavings in all the above.