4x4 engagement problem
 

I have a 98 Chevy K1500 with push button four wheel drive. When I am in 2 high the truck rolls fine but when I put it in 4 high or 4 low I hear and feel a horrible noise in the front end. I have been told it could be a universal joint, actuator, ect. How can I find out what the real issue is without spending money on parts I dont need?? Thank for any help at all

Explain noise a little better. Is it when your moving , or setting still. When you first put in 4 high? Thanks