01 Tahoe 4wd Problem

[krazykurt]

i just bought a 01 tahoe from a dealer when i go to put it into 4wd the light on the cluster dont come on but the little orange light says that its in 4wd. also when you can tell its in 4wd it makes a really weird like whining or grinding sound out of the front end when you have your foot on the gas when you take it off it goes away any ideas on what this can be or easy fix?