OK Let me get in on this one too. I first noticed the an extra transmission like noise while coasting over 40 just a few days before this issue was first posted. I have to turn the sound system below "normal" listening levels to hear it. But, it's definitely a new sound. I am at 20,000 miles on the odo. The front and rear diff and transfer fluids were changed at 15K dealer service.

Guess its truck?? And trucks make a lot of funny sounds??