2001 suburban 4x4 noise in front end

Just bought a 01 and tried out the 4x4 for the first time and it makes a noise and seems to pull to the left (friction) when it is in auto 4x4 it makes a continuous clunk noise over and over, when in 4hi/4low it seems to grind and causes the care to pull to the left.  What am I looking at?  Thanks for the help in advance.