I bought this truck about a month ago, every time I have it in 4x4 the front end makes whining noises and if you step on the gas it will make a cracking noise right underneath the drivers side. Is it the transfercase? U-Joints? Anyone else having this problem?

 

Check the oil in the front Differential Then check to see what is leaking. In most cases the drive shaft seal if so you will no doubt need a bearing. In a few cases one of the axles may be leaking. Also take a look at the U-joint the one next to the transfer case is strange. By the way the Transfer case is under the rear seat center & driver side.