Sierra 1500 Grinding When Turning Left In 4Hi

Hi, I'm kind of new to all this 4X4 stuff, but was curious about a problem that I have just noticed in my truck. I purchased the truck in September. It has roughly 72000 miles, and was possibly used for snow plowing. It is a V8, auto hubs, and does not have the Z71 Off Road Package. It is also equipped with the auto 4 wheel drive button. I haven't noticed the noise when I have that on, but I also haven't had to use it that much. There is an after market lift kit on it. The truck was making some rattling noises when I bought it, and the dealer fixed it. They replaced the steering shaft, and took some rocks from the slide pad(?) I believe in the transfer case. I have just had cause to start using the 4 Wheel drive, and have noticed a whining sound when I come to a stop, and also grinding or whines when turning left. I have only had it in 4 Hi so far. Also it was disclosed to me after buying the truck that it had sat for 180 days. From looking at the other questions on your forums, I'm thinking transfer case, but it's been suggested as well that it may be the Auto Hubs. I am a single mom, so any tips that you can give me on this would be greatly appreciated. :Roll: :)