Bought my wife an '02 Yukon XL with 40K miles. Has 2.5yrs and 32K miled remaining on ext warranty. Between 45 and 50 Mph, I am getting a very slight rear end whine. The whine immediately stops if you lift your foot from the pedal or once it passes 50 Mph. GM has replaced all rear end bearings and replaced the drive shaft with a "tuned shaft" which is addressed in a GM TSB. The noise is better but the GM cust svc guy drove it and said it was common with these trucks especially with those with 4:10 rear axles. Anyone experienced this? Again it is very slight and cannot be heard if the radio or air is blowing.

Bought my wife an '02 Yukon XL with 40K miles. Has 2.5yrs and 32K miled remaining on ext warranty. Between 45 and 50 Mph, I am getting a very slight rear end whine. The whine immediately stops if you lift your foot from the pedal or once it passes 50 Mph. GM has replaced all rear end bearings and replaced the drive shaft with a "tuned shaft" which is addressed in a GM TSB. The noise is better but the GM cust svc guy drove it and said it was common with these trucks especially with those with 4:10 rear axles. Anyone experienced this? Again it is very slight and cannot be heard if the radio or air is blowing.
Does it need lube?

Bought my wife an '02 Yukon XL with 40K miles. Has 2.5yrs and 32K miled remaining on ext warranty. Between 45 and 50 Mph, I am getting a very slight rear end whine. The whine immediately stops if you lift your foot from the pedal or once it passes 50 Mph. GM has replaced all rear end bearings and replaced the drive shaft with a "tuned shaft" which is addressed in a GM TSB. The noise is better but the GM cust svc guy drove it and said it was common with these trucks especially with those with 4:10 rear axles. Anyone experienced this? Again it is very slight and cannot be heard if the radio or air is blowing.
Does it need lube?

No, it is full of GM's $24.00 a qt synthetic lube.

I wouldn't worry about it. Some trucks just have noisy rear ends. My dad's pickup whined from day one to when he sold it a few years later. Never got worse or better. At the same time, you could just have noisy tires. If they have 40kmi on them they could be due for replacement anyway. Worn tires can cause symtoms of mechanical problems: whines, roaring, wobbling, etc. Something else to think about.

could also be the tranny...which it isn't all that uncommon to hear a whining transmission.

How loud is it? It sounds like no big deal to me.