Thanks both for the reply... I checked the diesel sound search results... not it. I'll read it in more detail but so far the symptoms are different. The sound itself is an even whine that stays at about same pitch no matter what speed, acceleration, coasting, etc... also, this is not motor related. My gut tells me it's probably the differential but don't have enough experience to know for sure.

Oh, and it's definitely not the tires or traction related, same "whine" occurs whether I'm at 2 mph, 20mph, or 40mph... can't hear the rest due to wind noise.

As far as slipping/jumpiness in tight turns - I had this truck for about 3 years now and pretty familiar with its eccentricities and character traits, especially in tight turns, on/off pavement, good/bad tires. What I'm experiencing now is very dissimilar in a feel and sound.

Thank you both for the input.