I have an 04 duramax and it has 102,000 miles on it. It started making a whining noise starting at 20 mph. I jacked up the rear with the front on the ground and it was making the noise so Its not the 4wd. The noise seems to come from the transfer case and the rear end. I checked the u-joints and they seem tight. Any Suggestions would be great!

Have you checked your oil levels?

yep, the axle and transfer case both are full:cool:

If anyone was wondering, the pinion bearing in the rearend went out. Those bearings are expensive!

I was wondering. Thanks !!