Front differential on 2002 GMC Yukon Denali

I have searched around and found out that the noise I am hearing from the front end of my Denali is possibly the Differential. It's a loud whinning noise when the vehicle is 20mph or faster in motion.

I need some insight and a estimate on the repair of such a problem

Asked by for the 2002 GMC Yukon Denali
it sounds like the bearings went bad. Depending on how many hard parts besides the bearings, the repair runs from $900 for just bearing work to $1500 for gear set replacement.
Dandd I have it in the shop now getting the gearbox replaced for about 1400..I guess you are right..Think I will have anymore problems in relation to that noise after replacing that?
Also what is the best way to prevent this from happening in the future??