When Im driving on the high way I hear like a whining noise its not that loud but when I let go of the gas it stops and I can also sometimes hear it passed 20-25 mph I think its the transfer case and if it is where can I find a better than factory transfer case?

 

Check the fluid level before just replacing it.

 

Usually a lot less whining if you leave the wife or GF at home.

 

Check the rear end fluid and driveshaft also.