2004 chevy trailblazer

my wife has a 04 chevy trailblazer ltd with 4wd i have a couple of questions “service 4wd” comes on seems stuck in 4wd has moaning noise over 20mph moaning goes away when turning has grinding noise coming from front and sometimes a clanking noise that doesnt sound like something heavy but not very light either

it could be a couple of things. 1. wheel bearings 2. u-joints 3. differential is bearings. I could be wrong but those are the first things that come to mind.

Is there a selector switch and what position do you leave it in? Sounds like the front transfer case to me. Do you rotate the tires?