2005 nissan xterra 4 wheel drive problem?

my 2005 nissan xterra has 4 wheel drive and it has been acting up for some time now. When i engage the 4 wheel drive and drive it feels like the front wheels are pulling faster than the back and causes me to drive worse on snow in 4 wheel drive. and also when i am driving in 4 wheel drive it makes a loud clanking sound and sounds like it is messing stuff up. Were suppost to get snow in a coulpe of days and i want to get it fixed but have no idea whats wrong with it. anything will help... Thanks!!!